National Academies Press: OpenBook

Future State of Smallpox Medical Countermeasures (2024)

Chapter: 2 State of Smallpox Medical Countermeasures Readiness

« Previous: 1 Introduction
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 41
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 42
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 43
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 44
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 45
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 46
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 47
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 48
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 49
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 50
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 51
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 52
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 53
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 54
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 55
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 56
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 57
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 58
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 59
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 60
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 61
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 62
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 63
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 64
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 65
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 66
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 67
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 68
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 69
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 70
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 71
Suggested Citation:"2 State of Smallpox Medical Countermeasures Readiness." National Academies of Sciences, Engineering, and Medicine. 2024. Future State of Smallpox Medical Countermeasures. Washington, DC: The National Academies Press. doi: 10.17226/27652.
×
Page 72

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2 State of Smallpox Medical Countermeasures Readiness “The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host.” John Connor, in presentation to the committee January 12, 2024, in reference to Olson and Shchelkunov (2003) A variety of medical countermeasures (MCMs) have been developed to detect (diagnostics), prevent (vaccines), and treat (biological agents and antivirals) smallpox disease and transmission. This section summarizes the key characteristics of these assets—focusing on gaps and future opportu- nities, including emerging technologies. One fundamental lesson learned from COVID-19 and mpox emergencies is that research and development for new smallpox MCMs must not only consider the characteristics of the “product” but also must consider the ability to deploy at scale and ensure equitable access. DIAGNOSTICS, DETECTION, AND SURVEILLANCE The ability to rapidly detect and diagnose a potential case of smallpox is central to all containment strategies. In the United States, the primary strat- egy for containment involves vaccination coupled with surveillance (Hen- derson and Klepac, 2013; Petersen et al., 2015). Outside of environmental detection systems for smallpox, which operate in limited capacity, the early identification of a smallpox case is presumed likely to occur based on clinical suspicion of smallpox or a non-variola orthopoxvirus. Clinical suspicion of 41

42 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES smallpox would be followed by testing for variola virus, whereas continued clinical suspicion of a non-variola orthopoxvirus for which non-variola orthopoxvirus testing is negative would require follow-on testing for the variola virus itself. In the United States, testing would be conducted by a U.S. Centers for Disease Control and Prevention (CDC) Laboratory Response Network (LRN) laboratory, with CDC conducting confirmatory testing on any positive samples with further confirmatory testing at CDC for any ini- tially variola virus–positive results (CDC, 2017b). As there are few practicing clinicians in the United States who have ever seen a person with smallpox, delays in diagnosis based on clinical suspicion are likely. Testing Options and Utility U.S. diagnostic testing options to confirm smallpox rely on a variola- specific assay approved by the U.S. Food and Drug Administration (FDA) in 2017. The FDA-approved Variola Virus Nucleic Acid-Based Detection Assay is indicated for “individuals presenting with pustular or vesicular rash ill- ness or other signs and symptoms of Variola virus infection” (FDA, 2024b). This is the only variola-specific assay available in the United States outside of CDC. This test is available at some LRN laboratories as part of a clini- cal testing algorithm, with positive results requiring confirmatory testing at CDC via single-gene PCR (polymerase chain reaction) testing and subse- quent confirmation via additional genomic testing (Hutchins et al., 2008). Electron microscopy (EM) or cell culture may additionally be used to provide evidence of an orthopoxvirus or indicate infectivity, respectively, however these techniques alone are not diagnostic for smallpox (CDC, 2016, 2017b). However, negative-stain EM is less sensitive than PCR, there are few laboratories with expertise in this technique, and its use may be limited to additional corroborative testing. Tissue and pathology sample evaluation with immunohistochemical staining is another diagnostic option. Gaps and System Pain Points Concerns with Clinical Recognition Capability The identification of smallpox cases requires clinical recognition. While clinician awareness of orthopoxvirus infections has increased in the United States due to the multi-country mpox outbreak, the rise of mpox could also obscure an outbreak of smallpox or another novel orthopoxvirus. A recent report describing the first fatal case of Alaskapox infection showed that over 6 weeks had passed between the patient’s first reported symptoms and a laboratory confirmation of Alaskapoxvirus (Rogers et al., 2024). Ad- ditionally, due to the low positive predictive value of smallpox diagnostics

SMALLPOX MEDICAL COUNTERMEASURES READINESS 43 in the absence of known disease,1 the identification of suspected and prob- able smallpox cases relies on a patient first meeting a clinical case defini- tion prior to testing (CDC, 2017a). These factors could hamper immediate identification of a smallpox outbreak, especially if case definitions are not appropriate or the initial cases present in an atypical fashion. For example, case definitions used in early days of the COVID-19 pandemic were overly strict by emphasizing travel to Wuhan, China (Suthar et al., 2022). Histori- cally, early waves of the smallpox outbreak in ex-Yugoslavia in 1972 where the index case had an atypical presentation without scarring (Ristanovic et al., 2016). During the 2022 mpox outbreak, once CDC and FDA began support- ing orthopoxvirus testing in five commercial laboratory companies, clini- cians preferred to use these laboratories over the public health laboratories of the LRN due to more streamlined patient data requirements and perhaps the perception of a more rapid availability of actionable results initially made possible by higher throughput testing capabilities at commercial laboratories (APHL, 2023). The addition of commercial laboratories also increased testing capacity significantly (CIDRAP, 2022). Better understand- ing of data needs and decision-making and distribution timelines could have implications for laboratory planning for an evolving smallpox out- break, especially around clinician education, the distribution and ubiquity of laboratory-based tests, and, critically for the questions posed to this committee, the level of investment by the Biomedical Advanced Research and Development Authority (BARDA) in point-of-care diagnostics for the U.S. Strategic National Stockpile (SNS) and for routine use. Limited Availability of Diagnostic Assays Diagnostic assays for variola are available only at select LRN labora- tories, largely due to biosafety considerations, and only as part of a clinical testing algorithm. The approach to only test at LRNs with confirmation at CDC may affect testing turnaround times during a larger outbreak. The cur- rent algorithm was designed for the detection of initial cases in the absence of endemic disease, but planning for laboratory capacity should include strategies for both immediate response and long-term scenarios where greater demand for testing arises. Greater availability of reliable laboratory- based tests for smallpox may enhance the nation’s ability to rapidly respond to a smallpox outbreak, although easier access to testing would also pre- sumably increase the frequency of false positive tests, making effective clini- cian education even more important. Additionally, expanding the number 1 For rare diseases, positive tests are more likely to be wrong than when the disease is commonly occurring.

44 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES of sites that can conduct both variola-specific and orthopoxvirus diagnostic testing would require concurrent improvements to laboratory biosafety and management of potential associated biosecurity concerns. Lack of FDA-Cleared Serological Assays FDA-cleared serological assays for smallpox have not been developed, and protein-based tests are still being explored. Lateral-flow assay tests so far do not offer high enough sensitivity to reliably detect orthopoxviruses and need further confirmation against clinical specimens (Ulaeto et al., 2022). Future Opportunities and Emerging Diagnostic Technologies The 2022 multi-country mpox outbreak spurred the development of nu- merous mpox and pan-orthopoxvirus diagnostics, which are now at various stages along research, development, or regulatory approval pathways. These include assets based on loop-mediated isothermal amplification (LAMP) technology, rapid diagnostics, serological assays, and a GeneXpert test; their potential effectiveness for smallpox has not been assessed. Numerous non-variola tests (e.g., mpox and pan-orthopox) developed by academic and commercial developers and used with FDA enforcement discretion policies could play an important role in a future smallpox event (FDA, 2023c). Many of these tests have been described in the literature, including real-time PCR assays used for mpox and an enzyme-linked immunosorbent assay (ELISA), for both IgG and IgM, used on subjects from Wisconsin, which was the epicenter of the 2003 U.S. mpox outbreak (Hammarlund et al., 2005; Karem et al., 2005; Y. Li et al., 2006). Any work which uses live variola virus to validate smallpox diagnostics must also be approved by the World Health Organization (WHO) Advisory Committee on Variola Virus Research (ACVVR). The lack of a sustained commercial market has likely deterred ongoing commitments for commercial assay developers. Develop Point-of-Care and Point-of-Need Tests Point-of-care (POC)/point-of-need (PON) tests for smallpox remain elu- sive.2 LAMP diagnostic assays, a relatively recent development in nucleic acid amplification, were developed and improved on during the 2022 mpox response and might be useful for POC testing in the event of a smallpox 2 POC test: clinical lab testing conducted close to the site of patient care where treatment will be provided. PON test: that provided at a location where an ill/exposed person can go to be tested and, if positive, go to a care site if needed. The PON test may be much more widely accessible than a POC test.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 45 outbreak, but they would need further real-world evaluation against the outbreak-causing strain (Z. Li et al., 2023). After 2022 FDA issued Emer- gency Use Authorizations (EUAs) for additional testing platforms, such as the Cepheid mpox assay (FDA, 2023d). Such advancements could aid in the development of future variola diagnostics particularly if developed for smaller multiplex platforms and equipment used within the clinical settings. These and other POC assays using protein or antigen-detection may be use- ful for initial testing to inform isolation and other public health decisions (Lewis, 2023; Meyer et al., 2020). Additionally, as has been noted with other high consequence pathogens, POC tests may also have a role to play in early evaluation of patients in resource scarce settings as well as use in mobile testing (Bhadelia, 2015; Castillo-Leon et al., 2021; Dhillon et al., 2015). Deployment of POC testing would need to be accompanied with patient and provider education about the limitations and use cases for these technologies, in partnership with public health authorities (Kost, 2021). Given the high public health concern regarding smallpox cases, rapid diagnostics aimed at the consumer are unlikely to have a role in most smallpox outbreaks. Expand PCR Assays and Platforms As discussed in Chapter 1, a limiting factor to expanding testing dur- ing the 2022 mpox multi-country outbreak was a lack of diverse testing assays and platforms at the beginning of the outbreak. Expansion of PCR assays and platforms, such as the development of pan-orthopoxvirus assays or variola-specific assays on a variety of platforms, could help reduce de- pendence on a single product, potentially reducing testing bottlenecks and increasing test accessibility. Additionally, platforms that can perform testing at different biosafety levels and at field sites would be useful in improving global access to testing. The Non-Variola Orthopoxvirus Real-Time PCR Primer and Probe Set is a pan-orthopox DNA test approved by FDA in 2022 to qualitatively detect all orthopoxviruses, except variola and Alaskapox viruses (FDA, 2024a; Rogers et al., 2024). The test cannot identify the specific non-variola orthopoxvirus that may be causing disease. This test was used for labora- tory diagnosis during the 2003 U.S. mpox outbreak response and has been used extensively since 2022. Additional PCR assays tailored for a range of platforms can increase the diversity of products available during an out- break and improve the ability to bring testing closer to the patients, while avoiding testing and manufacturing bottlenecks. In a potential outbreak, it is likely that the first patients evaluated for smallpox will already have rash illness and will have been infec- tious to others for several days prior to recognition. PCR testing can produce reliable results rapidly and is commonly used on lesion-based

46 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES samples including exudate, roofs from lesions, and lesion crusts (CDC, 2017b). During the mpox response, nucleic acid testing also found mpox in oral and naso-pharyngeal specimens, rectal tissue, semen, saliva, urine, and feces (Peiró-Mestres et al., 2022). Although the pathogenic mecha- nism for this observation may differ between clade IIb monkeypoxvirus infection and variola virus infection, this compares to reports of finding variola virus in saliva, conjunctiva, and urine in patients with hemorrhagic smallpox (Sarkar et al., 1973). Expanded availability of PCR testing in other sample types might allow for earlier disease identification and con- tainment, making it the preferred method for variola testing. Identification of biomarkers for presymptomatic detection of smallpox patients and im- provements to methodologies for automatic extraction methods for PCR testing could also be useful. Antibody testing utility is low, as for all acute illnesses, due to the time lag in antibody development, which results in poor prospects for early detection. There could be utility in using antibody titers as correlates of protection in those with prior vaccination and to understand population- level exposures and immunity to smallpox (Moss, 2011). Genomic and Environmental Surveillance While this report is primarily concerned with clinical screening and diagnostic tools that can support smallpox readiness and response, population-level and environmental surveillance tools and systems can also support preparedness and may rely on the same kinds of technologies and technological advances critical to clinical assay development. Genomic and environmental surveillance can be used to monitor shifts in circulating pox- virus genomes; information about such shifts may support predictions of increased or decreased virulence or transmission. Genomic surveillance dur- ing an outbreak supported by bioinformatics software, such as Nextstrain, can also provide critical feedback on real-time viral evolution (Hadfield et al., 2018). The environmental detection program, BioWatch, operated by the De- partment of Homeland Security, is designed to provide early alerts concern- ing aerosolized pathogens of concern by sampling air in strategic locations throughout the United States and coupling this with laboratory testing of the samples (IOM and NRC, 2011). Wastewater surveillance systems for disease detection were built in response to COVID-19 and were used for the detec- tion of mpox, mostly using PCR-based tests (Oghuan et al., 2023). Future expansion of wastewater surveillance to aircraft-based networks could po- tentially act as an early warning system (J. Li et al., 2023). Metagenomic ap- proaches to surveillance hold the potential to improve detection of pathogens that may not be normally suspected in a non-endemic area (Ko et al., 2022;

SMALLPOX MEDICAL COUNTERMEASURES READINESS 47 Sharma et al., 2023). Additionally, viral genomics and phylogenetic analyses have become important parts of public health investigations and are critical to stay ahead of pathogen evolution for emerging and priority pathogens and would be a critical component in the public health toolbox in case of a smallpox outbreak (Di Paola et al., 2020; Saravanan et al., 2022). Conclusions on Diagnostics, Detection, and Surveillance (2-1) Tests that can more accurately detect smallpox and other orthopoxviruses than those available today are needed; efforts should focus on (1) adapting multiplex nucleic acid assays for new platforms and field settings, (2) develop- ing forward-deployed (POC/PON) assays to enhance equitable access to tests, including protein or antigen-based tests to rapidly test and isolate infected patients, (3) identifying FDA-approved serologic assays to assess individual and population levels of immunity against smallpox and history of related exposures, (4) validating nucleic acid testing using a variety of clinical samples, (5) developing different categories of laboratory tests for different biosafety levels, and (6) supporting a global network of laboratories to detect, diagnose, and conduct surveillance in humans and the environment. VACCINES As observed in the early phases of the smallpox eradication program, robust surveillance and containment strategies implemented concurrently with ring vaccination—the targeted vaccination of contacts of cases, con- tacts of contacts, and others at high risk of exposure—was paramount to mitigating or eliminating human-to-human transmission (IOM, 2002; Lane, 2006). A ring-vaccination-based containment approach was effec- tive to eradicate naturally occurring smallpox due to the long incubation period of smallpox (and mpox) in humans. This made ring vaccination for smallpox and mpox, even after exposure, epidemiologically, clinically, and economically efficient at mitigating or eliminating illness and subsequent transmission compared with mass vaccination (Foege, 2011; Sah et al., 2022). Ring vaccination is also still recommended by both WHO and CDC as the first-line response strategy for a smallpox outbreak (CDC, 2019b; WHO, 2023). However, both CDC and the WHO Strategic Advisory Group of Experts on Immunization (SAGE) note that the scale of vaccination (from ring vaccination to mass vaccination) may be determined based on risk and the outbreak characteristics and the groups needing vaccinated. For a bioterrorist attack, particularly one occurring in a populous city, mass vaccination post-event, or following an immediate response to contain spread, has also been discussed as an effective strategy. Models and simula- tion exercises from the early 2000s highlighted logistical challenges and the

48 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES inability for ring vaccination to be scaled rapidly enough post-event to be effective (Bicknell, 2002; Kaplan et al., 2002). In the early 2000s, preemp- tive mass vaccination also carried greater risk of adverse events, compared to the limited benefits afforded when the threat of a bioterrorist attack remained small (Fauci, 2002). Uncertainties in the expected need to provide smallpox vaccine for the entire population makes it reasonable to plan for scenarios where the entire population needs vaccination. However, planning considerations would need to reflect more recent population characteristics and increasing po- tential for de novo synthesis or deliberate engineering to cause a smallpox event (see Chapter 2). The Institute of Medicine’s (IOM’s) previous reports Live Variola Virus: Considerations for Continuing Research (2009) includes a detailed summary of the history of smallpox vaccine development—from early vaccine develop- ment to post-eradication era—and describes how the development of smallpox vaccines has progressed in major phases (first-, second-, third-generation) (IOM, 2009). The effectiveness of vaccines developed post-eradication to prevent disease, transmission, hospitalization, or death in the event of a small- pox or novel orthopoxvirus outbreak will remain unknown due to the inabil- ity to test vaccine effectiveness against active smallpox infections. Licensure for newer vaccines must rely on non-inferiority data for immunogenicity and protection in animal challenge models compared with first-generation or second-generation smallpox vaccines. This challenge also highlights the impor- tance of being able to rapidly deploy adaptable clinical trials if an outbreak does occur (see Chapter 4 for more details on research readiness). Vaccine Options and Utility Currently, the U.S. stockpile maintains three different smallpox vac- cines, all of which are based on vaccinia virus: two types of live, replicat- ing virus vaccines; and an attenuated live, non-replicating vaccine as well as ancillary supplies for their administration (Table 2-1). The two types of replication-competent vaccinia virus vaccines in the SNS are Smallpox (Vaccinia) Vaccine, live (ACAM2000), which is a second-generation vaccine based on the first-generation vaccine Dryvax, and Aventis Pasteur Smallpox Vaccine (APSV), or WetVax, which is a first-generation vaccine (i.e., liquid formulation of calf-lymph-origin vaccinia virus vaccine) that was manufac- tured from 1956 to 1957 and has been maintained at −20°C (CDC, 2019a; Petersen et al., 2015). APSV is intended to be used only after ACAM2000 is exhausted, its potency is verified, and if approved for use in a small- pox emergency under an appropriate regulatory mechanism, specifically an EUA or an investigational new drug (IND) application (CDC, 2022). Live, replicating vaccinia virus vaccines are expected to be used to contain

SMALLPOX MEDICAL COUNTERMEASURES READINESS 49 TABLE 2-1  Summary of Smallpox Vaccines in the U.S. Strategic National Stockpile Product Name Characteristics Approved Usage Formulation and Storage APSV (Wetvax) 1st generation • Emergency Use Formulation contains Live, replicating Authorization (EUA)/ live vaccinia virus in vaccinia virus, Investigational New Drug 50% glycerol, 0.4% NYCBOH-derived (IND) for smallpox. phenol, 0.00017% strain. • 1 dose regimen. Brilliant Green, and • Multiple frozen at −20°C. contraindications, especially for those who have immunocompromising, skin, or heart conditions. Contraindicated for those with serious allergy to a vaccine component. ACAM2000 2nd generation • FDA licensed for Lyophilized (1 × Live, replicating prevention of smallpox in 108 pfu/ml when vaccinia virus, all age groups for those reconstituted), diluent is NYCBOH-derived at high-risk for smallpox 50% Glycerin USP and strain. infection. 0.25% phenol USP in • 1 dose regimen. water, stored at −20°C. • Multiple contraindications, especially for those who have immunocompromising, skin, or heart conditions. Contraindicated for those with serious allergy to a vaccine component. MVA-BN 3rd generation • FDA licensed for Liquid, 10mM Tris, (Imvamune, Live, smallpox and Mpox in 140mM sodium Imvanex, non-replicating adults 18 and older. chloride, host cell DNA JYNNEOS) vaccinia virus, • 2 dose regimen, (≤20mcg) and protein MVA strain. 4 weeks apart. (≤500mcg), benzonase • Relatively few (≤0.0025mcg), contraindications. gentamicin Safely administered (≤0.400mcg), to individuals with and ciprofloxacin immunocompromising, (≤20.005mcg), stored skin, or heart conditions. frozen at −25°C to Contraindicated for those −15°C. with serious allergy to a vaccine component. SOURCES: Adams (2023); FDA (2021a, 2022); Petersen et al. (2015)

50 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES transmission following a deliberate or accidental release of smallpox, as well as for a post-event vaccination program (Petersen et al., 2015). These vaccines are also the predominant type among the current cached vaccine assets and are intended to be available in sufficient quantity for the entire U.S. population (Adams, 2023). Non-replicating vaccines were acquired more recently to provide an alternative for individuals contraindicated to receiving replicating smallpox vaccine. Modified vaccinia Ankara vaccine-Bavarian Nordic (MVA-BN), marketed in the United States as JYNNEOS and elsewhere as Imvamune, or Imvanex, is a third-generation live, non-replicating vaccine developed in collaboration with the U.S. government. MVA-BN was developed post- eradication, and therefore not tested in a smallpox endemic setting. Studies using first-generation vaccine as a challenge, found that MVA-BN vaccina- tion prior to vaccination with Dryvax decreased the primary cutaneous reac- tion and decreased the time to healing, suggesting that MVA-BN would be protective against smallpox (Frey et al., 2007; Parrino et al., 2007; Pittman et al., 2019; Seaman et al., 2010). A phase 3 trial also observed fewer adverse events among those who received two doses of MVA-BN compared to indi- viduals who only received Dryvax (Pittman et al., 2019). The Department of Health and Human Services (HHS) has procured MVA-BN for the SNS at smaller volumes than first- and second-generation vaccines and intends to use it primarily for populations with contraindications to those vaccines (Wolfe, 2023). Additionally, the utility of MVA-BN in a ring vaccination strategy for immediate containment has not been demonstrated due to the use of a two-dose regimen. In 2023 the Advisory Committee on Immuniza- tion Practices updated recommendations for the use of MVA-BN in adults at risk for mpox, and the Strategic Advisory Group of Experts on Immuni- zation recommended that WHO add MVA-BN to its stockpiles and review protocols for smallpox (CDC, 2023a; WHO, 2023). The level of humoral antibody needed to provide protection against smallpox following vaccination is unknown. Data from eradication efforts suggested that a neutralizing antibody titer of more than 1:20 or more than 1:32 resulted in some level of protection against symptomatic illness (Mack et al., 1972). Currently licensed vaccines could not, for ethical reasons, in- clude human vaccine efficacy trials. Therefore, vaccines were licensed using neutralizing antibody titer equivalence. The true efficacy as well as the du- ration of immunity is unknown, as was the case during the pre-eradication era. It is believed that persons who had past exposure to variola virus or received only primary immunization would have lifelong protection from fatal infection (Taub et al., 2008). Box 2-1 provides an overview of the characteristics of first-, second-, and third-generation vaccines as well a placeholder for potential fourth- generation vaccines, which are expected to provide improvements in safety, efficacy, administration, or other key characteristics.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 51 BOX 2-1 Smallpox Vaccine Summary and Terminology First Generation (e.g., Dryvax, APSV) • Live vaccinia virus vaccines developed before and during the smallpox eradi- cation effort. • Typically produced by infecting large animals and collecting, purifying, and lyophilizing the lymph exudate. • Administered percutaneously using a bifurcated needle as a single dose. • Characteristic “take,” or scar develops at vaccination site. • Estimated high efficacy rates (typically >91%). • Side effects and adverse events vary by virus strain. • Multiple contraindications, especially for those who are immunocompromised or have skin or heart conditions. Second Generation (e.g., ACAM2000) • Live vaccinia virus vaccines developed using clonal derivatives of 1st genera- tion vaccines (Dryvax). • Produced in mammalian cell culture or in embryonated eggs using good manufacturing practice (GMP) methods. • Administered percutaneously using a bifurcated needle as a single dose. • Characteristic “take,” or scar develops at vaccination site. • Similar immunogenicity to 1st generation vaccines. • No efficacy data available against smallpox (developed after eradication). • Fewer side effects and adverse events than 1st generation vaccines. • Multiple contraindications, especially for those who are immunocompromised or have skin or heart conditions. Third Generation (e.g., MVA-BN) • Vaccines containing highly attenuated live vaccine or non-replicating strains of vaccinia virus. • Produced in mammalian cell culture, embryonated eggs, or Chicken Embryo Fibroblast cells (e.g., for MVA-BN specifically) using GMP methods. • Administered by injection. • MVA-based formulations require two doses, at 0 and 4 weeks, do not induce formation of a “take.” • Immunogenicity after all doses (i.e., non-inferior to 1st and 2nd generation vaccines). • No efficacy data available against smallpox (developed after eradication). • Far fewer side-effects and adverse events than 1st and 2nd generation vaccines. • Relatively few contraindications. Safely administered to individuals with HIV, cancer patients, organ transplant recipients, and individuals on immunosup- pressive therapies. continued

52 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES BOX 2-1  Continued Fourth Generation (none currently licensed or stockpiled; in clinical develop- ment only) • Potential subunit or nucleic acid vaccines (protein, peptide, mRNA) lacking replicating vaccinia virus. SOURCES: CDC (2023c); Kennedy and Gregory (2023); Petersen et al. (2015). Gaps and Pain Points Safety Concerns and Adverse Events The safety profiles of ACAM2000 and APSV (Wetvax) are expected to be similar to Dryvax (first-generation vaccine), as both vaccines are based on the New York City Board of Health (NYCBOH) strain used in Dryvax (Petersen et al., 2015). Adverse events, though rare, can be severe and life- threatening (Table 2-2). Historical data indicate that first-generation vac- cines were associated with at least 1 death per million primary vaccinations given, with the higher frequency of adverse events arising following primary vaccination and in younger children (Belongia and Naleway, 2003). It is important to note however that these data come from a period when small- pox vaccines were administered within the first months of life, knowledge of cell-mediated immunity was lacking, and some contraindications could not be accurately diagnosed in young infants. More recently, a voluntary smallpox vaccination program implemented in 2002 using second-genera- tion vaccines among military personnel and civilians was discontinued by June 2003 due to cases of myo/pericarditis, concerns of viral shedding and risk of vaccinia infection to others, and at least three deaths (IOM, 2005). CDC’s clinical use guidelines for smallpox vaccine indicate that there are no absolute contraindications for a smallpox vaccination in a post-event setting but that there are certain “relative” contraindications due to the possibility of adverse events associated with certain conditions (Table 2-2). CDC developed its recommendations for smallpox use by weighing risk for smallpox infection, risk for an adverse event following vaccination, and benefit from vaccination (Petersen et al., 2015). Relative contraindica- tions include atopic dermatitis (eczema), HIV infection (CD4 cell counts of 50–199 cells/mm3), other immunocompromised states, and allergies to the vaccine or vaccine components. The adverse events can range from general- ized vaccinia, a rash resulting from spread of the replicating virus from the injection site, to myopericarditis and death. The rates of these events are variable and, in some cases, unknown (Table 2-2).

SMALLPOX MEDICAL COUNTERMEASURES READINESS 53 TABLE 2-2  Potential Adverse Events Associated with Smallpox Vaccination with Replicating Vaccine Historical Risk of Adverse Event Description Complication Auto-inoculation Transfer of the virus from the injection 0–1647 per million site to another site on the body or to primary vaccinations another individual. Lesions occur on new site with the same progression as 0–675.7 per million the vaccine site. If transferred to the eye, revaccinations vaccinia keratitis, corneal scarring, and blindness can occur. Bacterial infections Bacterial infection of the vaccination No historical frequency site; typically, staphylococci or group data reported. A streptococci. Can be minimized by appropriate vaccine site care. Typically responds well to antimicrobials. Congenital vaccinia Infection in utero can occur after ~10–100 per million vaccination of pregnant women. vaccinations Exceptionally rare and results in stillbirth or death of the newborn shortly after birth. Death Typically, due to post-vaccinal Historically reported as encephalitis (fatality rate = 25%), 1–2 deaths per million progressive vaccinia (fatality rate primary vaccinations. nearly 100% and eczema vaccinatum Often in young children or (10% before vaccinia immune globulin those with unrecognized [VIG], 2% afterward). defects in T cell immunity. Eczema vaccinatum Large areas of the skin become covered 8.1–96.8 per million in confluent lesions. Untreated, this can primary vaccinations lead to systemic symptoms and septic shock. VIG treatment is effective if given 0–13.5 per million within 1–2 days of symptom onset. This revaccinations adverse event is seen in recipients with underlying skin conditions (eczema, atopic dermatitis) even without active disease. Generalized vaccinia Viremia and rash spreading from 20.8–387.1 per million vaccination site or occurring elsewhere primary vaccinations on the body. Most cases resolve without treatment. VIG can be used, as can 0–9.0 per million treatment appropriate for known revaccinations immune abnormalities. Myopericarditis Inflammation of the heart muscle or the Not assumed to be pericardium/pericardial space. Can be vaccine-related and accompanied by shortness of breath, therefore not well chest discomfort, or pain. Symptoms documented during occur 4–30 days after vaccination. eradication era. continued

54 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES TABLE 2-2 Continued Historical Risk of Adverse Event Description Complication Post-eradication data from military populations indicate a rate of 80–160 cases per million primary vaccine recipients. Reports focusing on civilian populations have a higher rate ~500 cases per million vaccinees. Non-infectious Generalized rash occurring 1–2 weeks 51.5–164.6 per million rashes (erythema after vaccination. Most resolve primary vaccinations multiforme) spontaneously and can be managed by over-the-counter treatments. Rarely, they 2.1–10 per million can result in hospitalization. Stevens- revaccinations Johnson syndrome and death have also been reported. Post-vaccinal Encephalitis occurs 1–2 weeks after 1.5–176.5 per million encephalitis vaccination, causing one or more of primary vaccinees the following: headache, drowsiness, vomiting, muscular weakness, ataxia, 0–2 per million paralysis, coma, convulsion. Has re-vaccinees a fatality rate of 25%. In 50% of survivors, some degree of neurologic damage is present, which can be permanent. No known predictors of susceptibility markers. VIG is not effective. Progressive vaccinia Characterized by a failure of vaccine 0–6.9 per million primary (disseminated site to heal, progressive spreading of the vaccinations vaccinia, vaccinia lesion in the absence of inflammation, necrosum) viremia leading to additional lesions 0–6 per million on distal sites that follow the same revaccinations progressive spread. Believed to be a result of a defective or inadequate T cell response. Bacterial infection is common, and patients can suffer from toxic or septicemic shock. Treatment with VIG was used in the 1960s with partial success. Recently developed antiviral drugs (e.g., Cidofovir or ST-246) may be effective. SOURCES: Aragón et al. (2003); Arness et al. (2004); Engler et al. (2015); Lane et al. (1969, 1970); Morgan et al. (2008); Murphy et al. (2003); Neff et al. (1967a,b); Ratner et al. (1970); Ryan et al. (2008); Tack et al. (2013).

SMALLPOX MEDICAL COUNTERMEASURES READINESS 55 Due to this potential for severe adverse events in certain immunocom- promised persons, CDC recommends that people with relative contraindi- cations be vaccinated with MVA-BN. Clinical trials involving healthy and high-risk populations, such as those with HIV infection, have reported no cases of myo-/pericarditis after vaccination with MVA-based vaccines, whereas myo-/pericarditis was observed with the use of first-and second- generation live smallpox vaccines (Overton et al., 2015; Zitzmann-Roth et al., 2015). The rates and severity of mostly mild, self-limiting common side effects (e.g., headache, fever, myalgia, regional lymphadenopathy) are broadly similar for MVA-BN and ACAM2000. The main disadvantages of MVA-BN in a post-event setting are that it re- quires two injections given 4 weeks apart, and, unlike replicating vaccines, its real-world efficacy against smallpox is unknown and has been assessed only through animal models, serological endpoints, and non-inferiority studies. Vaccination campaigns using non-replicating MVA-BN to vaccinate persons at risk of mpox provide additional valuable data and demonstrate effective- ness rates for two doses ranging from 66 percent to 86 percent (Dalton et al., 2023; Deputy et al., 2023; Rosenberg et al., 2023). While MVA-BN is safe for immunocompromised persons and should provide protection for those at risk of eczema vaccinatum, effectiveness in severely immunodeficient populations is expected to be lower due to inability to mount an effective immune response after vaccination (CDC, 2023b). However, it is unknown whether an exposure dose–response or exposure based on differing modes of transmission (e.g., sexual contact related disease vs. other modes of mpox transmission) is associated with observed vaccine efficacy. Reliance on the U.S. Strategic National Stockpile and Concerns with Manufacturing Capacity Dependence on the SNS smallpox vaccine stockpile as the primary form of smallpox readiness has required that sufficient inventory be maintained to respond to a smallpox event where the entire U.S. population could potentially require vaccination. This explains, in part, the large proportion of spending that has gone to smallpox MCM. Under the current stockpil- ing strategy, ACAM2000 will be the primary vaccine used in a smallpox response scenario. While older second-generation vaccines in the SNS are thought to be quite stable, their potency is less well understood, and MVA- BN had been intended to be used for only a subset of the population. While quantities of stockpiled vaccine doses are not released publicly, research estimates put the U.S. immunocompromised population (the main popula- tion for which MVA-BN is intended) at approximately 15 percent of the population, more than 49 million people, rising to about 38 percent if their household contacts are included (Adams, 2023; Carlin et al., 2017).

56 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Notably, this figure does not include the population with post-acute sequelae of SARS-CoV-2 (long COVID), who appear to have immune dysfunction following COVID-19 infection, though the committee found no evidence that such a state would be an absolute or relative contraindication to live smallpox vaccination (Phetsouphanh et al., 2022). The risks and benefits of live vaccine for the heterogeneous immunocompromised population must be weighed. Finally, a likely approach to contain a smallpox outbreak would be to use both vaccines and therapeutics. However, the potential interac- tions between vaccines and antivirals if used concomitantly are not well understood (Russo et al., 2020). The choice to focus on stockpiling vaccines has been driven, in part, by limited production capacity, which makes it difficult to rapidly manufacture additional smallpox vaccine doses. Smallpox vaccines are not mass-market vaccines that are produced in a routine manner using widely available ingre- dients and common manufacturing processes. Ramping up the production of smallpox vaccines to meet a sudden demand would require procuring potentially limited raw materials and navigating multiple regulatory and safety hurdles. Future Opportunities and Emerging Vaccine Technologies Opportunities for newer vaccines include the development of those with fewer contraindications, broad protection, single-dose administra- tion, and stable shelf-life. As noted by the WHO ACVVR, the development of “scalable less-reactogenic vaccines” with improved efficacy and dura- bility of protection would be “essential for the control of an outbreak of smallpox in the current context, should it recur” (WHO, 2024). Research on fourth generation smallpox vaccines could explore potential subunit or nucleic acid vaccines (protein, peptide, mRNA) lacking replicating vaccinia virus. Explore Innovative Vaccine Platforms Safe and effective COVID-19 vaccines were made in under a year since the start of the pandemic due to decades of research on mRNA vaccines and U.S. government investment in mRNA platform technology (NIH, 2022). Smallpox vaccine development could benefit from investments in novel, rapid vaccine platforms such as mRNA, viral vectors, and protein nanopar- ticles. Like for most potential vaccine targets, mRNA technology may be a useful approach; however, the utility of this approach, specifically for or- thopoxviruses remains uncertain. There is work underway evaluating novel mRNA constructs, however (Hou et al., 2023), and the National Institutes of Health (NIH) is supporting the development of mRNA-based vaccines for

SMALLPOX MEDICAL COUNTERMEASURES READINESS 57 orthopoxviruses (Freyn et al., 2023; HHS, 2023). Modified vaccinia Ankara (MVA) has also shown utility as a vaccine vector for non-orthopoxvirus pathogens (e.g., HIV, malaria, Ebola, tuberculosis, MERS-CoV) as well as in oncolytic virotherapies (Lin et al., 2023; Orlova et al., 2022). While any vaccine using the MVA backbone would provide some protection against smallpox and other orthopoxviruses, the utility of recombinant MVA vac- cines to contain a smallpox emergency is uncertain. Develop Immunobridging Strategy Development of an immunobridging strategy would be important to allow for useful cross-vaccine comparisons, especially as there is no way to effectively test a smallpox vaccine for efficacy against smallpox. This type of approach has been considered for COVID-19, filovirus as well as for seasonal influenza vaccines (Gruber et al., 2023; Khoury et  al., 2023). Basic clinical trials for safety and immunogenicity can be accomplished through routine clinical development strategies along with relevant antecedent preclinical studies. Further work into the utility of fourth-generation vaccines that use multi-vaccine platforms and immu- nobridging strategies would allow for greater diversity in the vaccine products that are available. Diversification of MCM products in the SNS is highlighted in Chapter 4. Conclusions on Vaccines (2-2) Smallpox vaccines that have improved safety across different population subgroups and are available as a single dose would support faster and more ef- fective response to contain smallpox and other orthopoxvirus outbreaks. The development of novel smallpox vaccines using multi-vaccine platforms (i.e., use common vaccine vectors, manufacturing ingredients, and processes) would improve the capacity for rapid vaccine production in response to a smallpox event and reduce the need for stockpiling in the SNS at current levels. THERAPEUTICS Initiated in the late 1990s, the initial approach to developing smallpox treatments was to screen small molecule compounds and further develop those that demonstrate activity across orthopoxviruses (OPXVs) (Baker et al., 2003). More recent efforts have evaluated anti-variola and anti- orthopoxvirus activity with a focus on biologics, such as monoclonal an- tibodies, antibody cocktails, and vaccinia immunoglobulin (VIG), as well as antivirals with distinct mechanisms of action (Martins, 2023). Table 2-3 presents a summary of smallpox antivirals with additional details on their mechanisms of action, indications, bioavailability, and storage.

TABLE 2-3  Summary of Smallpox Therapeutics in the U.S. Strategic National Stockpile 58 Product Name Mechanism of Action Indication Bioavailability Formulation and Storage Tecovirimat Orthopoxvirus-specific • Treatment of smallpox (FDA • Oral formulation: 48% Capsules stored in the (ST-246/TPOXX) inhibition of viral spread approved) oral bioavailability with original bottle at 20°C from cell to cell by • Other uses for treatment of enhanced absorption to 25°C (68°F to 77°F); targeting p37, a major mpox under Investigational New when taken with food excursions permitted envelope protein required Drug (IND), Expanded Access (DeLaurentis et al., 2022). 15°C to 30°C (59°F to for envelopment and IND, Emergency IND (not FDA The FDA approval is for 86°F). excretion of extracellular approved) oral administration within forms of the virus. • STOMP/A5418 (Study of 30 minutes of a moderate- Injection stored at 2°C to Tecovirimat for Human to high-fat meal. Maximum 8°C (36°F to 46°F). Mpox Virus)a concentration is at 4 hours • STOMP sub-study of open post oral dose. FDA had initially label tecovirimatb • IV formulation: Max approved a shelf-life • STOMP sub-study: concentration at the end of extension of tecovirimat Tecovirimat for Orthopox recommended infusion given injection from 24 months Virus Exposurec over 6 hours. to 42 months for some lots (FDA, 2023b). Brincidofovir Pro-drug of cidofovirf; • Treatment of human smallpox • The lipid modification Oral suspension—expiry (CMX001/ following phosphorylation infections only (FDA approved) of cidofovir that created 30 months from the Tembexa) of the prodrug to the • Other usesd (EIND or EA IND): this drug enhances its date of manufacture active form cidofovir • Study to Assess Brincidofovir oral bioavailability in when stored at 20°C diphosphate which targets Treatment of Serious Diseases oral tablet and suspension to 25°C (68°F to 77°F) the orthopoxvirus DNA or Conditions Caused by formulations. (FDA, 2021b). polymerase, causing Double-Stranded DNA • The tablet has 13.4% disruption of replication of virusese (phase 3 completed bioavailability whereas Tablets—expiry the virus. December 2022) the suspension has 16.8% 48 months from the date • Adenovirus in immuno- bioavailability. of manufacture when compromised persons: under • Best absorption is when stored at 20°C to 25°C clinical trial taken on an empty stomach (68°F to 77°F). or with a low-fat meal.

Vaccinia Immune Passive immunity • Treatment of complications due • Maximum concentration Stored frozen at or Globulin for individuals with to vaccinia vaccination (FDA at 6,000 U/kg dose reached below 5°F (≤ –15°C) Intravenous complications to vaccinia approved) in 1.8 ±1.2 hours, and or refrigerated at 36°F Human (VIGIV) virus following vaccination; • Other uses (EA IND): Potential with 9,000 U/kg dose was to 46°F (2°C to 8°C); (CNJ-016) exact mechanism of action use of stockpiled VIGIV for reached at 2.6 ±2.4 hours if received frozen, is not known. treatment of orthopoxviruses in after administration. use within 60 days of an outbreak • Available upon clinician thawing at 36°F to 46°F request to CDC on case-by- (2°C to 8°C). case basis for intravenous administration. NOTES: Cidofovir (Vistide), another antiviral not currently stockpiled, targets orthopoxvirus DNA polymerase, causing disruption of replication of the virus. The licensed indication is for cytomegalovirus (CMV) retinitis and does not have licensed indication for OPXV/VARV therapy. However, it can be used “off label.” Cidofovir was used in therapy of mpox in those with compromised immune systems/uncontrolled HIV during the 2022–2023 multi-country outbreak, as this treatment was commercially available. Potential side effects include renal toxicity. CDC = U.S. Centers for Disease Control and Prevention; EA = expanded access; EIND = emergency investigational new drug application; IND = investigational new drug application; OPXV = orthopoxvirus; VARV = variola virus. a NIH/NIAID-sponsored: Phase 3 randomized, placebo-controlled, double-blind study to establish the efficacy of tecovirimat for the treatment of people with laboratory-confirmed or presumptive human monkeypox virus disease (HMPXV) [NCT05534984]. b Open label for pregnant or breastfeeding persons; those with severe immune suppression, significant skin conditions, or severe disease. c For both mpox and smallpox for Department of Defense–affiliated personnel [NCT02080767]. d There are no registered clinical trials for brincidofovir at this time, could be used under EIND through CDC. e Phase 3 trial completed 12/2022 with posted results [NCT01143181]. f Cidofovir was used in therapy of mpox in those with compromised immune systems/uncontrolled HIV during the 2022-2023 multi-country out- break, as this treatment was commercially available. SOURCES: Chan-Tack et al. (2021); Emergent BioSolutions Canada Inc. (2018); Gilead Sciences (2000); Grosenbach et al. (2011, 2018); Huston et al. (2023); Jordan et al. (2010); Merchlinsky et al. (2019); Yang et al. (2005). 59

60 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Potential smallpox therapeutics can only be tested in vitro against va- riola virus or by using nonhuman animal models or surrogate viruses (e.g., non-variola virus). Such testing data, coupled with pharmacokinetic and safety data in humans, has allowed for FDA approval of tecovirimat and brincidofovir under the Animal Rule pathway (FDA, 2023a). Additionally, in many studies assessing the efficacy of antivirals against mpox in small animals, therapeutics were administered prior to the onset of rash illness (Hutson and Damon, 2010). More recent efforts have looked at therapeutic efficacy in nonhuman primates when initiated after rash onset following exposure to mpox (Russo et al., 2018). Because clinical guidelines rely on the presentation of rash illness to collect specimens for testing and to iden- tify probable smallpox cases, the effectiveness of these therapeutics against the most likely early case presentations (i.e., people with a smallpox rash) is uncertain. Experience with the mpox outbreak revealed that those with severe immunosuppression required extended courses of treatment, often using multiple therapeutics (Pinnetti et al., 2023). Therapeutics Options and Utility Smallpox antiviral research and development efforts to date have re- sulted in two antiviral agents that are FDA approved for the treatment of human smallpox in adult and pediatric patients: tecovirimat and brincido- fovir (CDC, 2023d,e). These products have different mechanisms of action and oral bioavailability (see Table 2-3). Both tecovirimat and brincidofovir were approved under the Animal Rule and must be requested from the SNS, as neither is commercially available. Tecovirimat is efficacious as a post-exposure therapeutic treatment of orthopoxvirus, specifically mpox, and its utility as a pre-exposure prophylaxis in high-risk humans is likely following observed therapeutic benefits in nonhuman primates evaluated in a prelesional and postlesional setting (Mucker et al., 2013). Cidofovir, a commercially available drug approved by FDA in 1996 for the treatment of AIDS-related cytomegalovirus (CMV) retinitis, was also used “off label” to treat mpox in immunocompromised individuals during the 2022 multi- country mpox outbreak (Siegrist and Sassine, 2023). Cidofovir has a more severe side effect profile than brincidofovir and is only recommended when the latter is not readily available. Gaps and Pain Points Lack of Diverse Antivirals The two approved antivirals have independent mechanisms of action and are not antagonistic of each other. While brincidofovir slows DNA

SMALLPOX MEDICAL COUNTERMEASURES READINESS 61 synthesis, tecovirimat inhibits membrane protein p37 that is essential for formation of an enveloped virus, so both could be used in combination (Siegrist, 2023). However, the effectiveness and utility of combination thera- pies to improve treatment efficacy and reduce the potential of anti-viral resistance are yet to be determined (P. Li et al., 2023). Periodic evaluation of compound libraries may ultimately yield additional promising therapeutics. Additionally, it would be ideal to have antivirals that act upon different stages of the virus lifecycle, (e.g., targeting specific virion components or other steps of viral infection) to mitigate the potential for antiviral resis- tance (Delaune and Iseni, 2020). Finding drugs that target and kill only the virus without damaging host cells is also a challenge because viruses use the host’s cell to replicate (Kausar et al., 2021). In addition to considering the mechanisms of action, diverse modes of antiviral administration might provide increased protection. In one study, aerosolized cidofovir was found to protect mice against an otherwise lethal challenge of aerosolized cowpox virus (Bray and Roy, 2004). A similar approach could be possible with aerosolized brincidofovir as well. Concerns with Antiviral Resistance and Adverse Events Antiviral resistance is a significant concern for the current antivirals. Stepwise resistance to cidofovir is known to occur when treating CMV, with moderate resistance with single mutations and a higher level of re- sistance with multiple mutations (Siegrist and Sassine, 2023). Notably, cidofovir-resistant virus is less virulent than wild type (CDV-sensitive) virus. Whether this would occur in the setting of monkeypox (MPXV) or VARV is unknown. With tecovirimat and brincidofovir, single amino acid resistance mutations have been observed, with questionable impacts on viral fitness (Foster et al., 2017; Smith et al., 2023). Adverse events, such as serious renal toxicity, have been observed dur- ing treatment of CMV retinitis infections with cidofovir (Skiest et al., 1999). Additionally, intravenous tecovirimat is not recommended for patients with severe renal impairment (CDC, 2023d). Future Opportunities and Emerging Therapeutic Technologies Research and development efforts in the past 10 years have often focused on re-purposing non-vaccine biologics and antibody-derived therapeutics: • Vaccinia immune globulin intravenous (VIGIV) is a polyclonal anti- body therapy and FDA-licensed biological agent (since 2005) for the treatment or modification of complications resulting from vaccinia smallpox vaccination (CDC, 2023c). There is potential to repurpose

62 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES this biologic for treatment of orthopoxviruses in an outbreak, however VIGIV has not been considered an effective standalone therapeutic for smallpox (Jahrling 2011). In response to the 2022 multi-country outbreak, expanded access for VIGIV was provided through an In- vestigational New Drug (IND) Application to treat mpox infection in adults and children in concert with small molecule compounds; however, data on efficacy are limited (Gilchuk et al., 2016). • BFI-753 (Biofactura), a two-antibody cocktail to treat smallpox, is in late preclinical development, with an anticipated IND applica- tion submission in 2025 (Martins, 2023). • Preclinical studies on potential therapeutics targeting cellular pro- teins or systems required for the virus lifecycle, such as imatinib me- sylate (Gleevec®), have not progressed past early-stage research and development efforts, as concerns remain about imatinib’s potential for treating smallpox (Ananthula et al., 2018; IOM, 2009; Reeves et al., 2005, 2011). For example, animal model benefit required con- tinuous pump infusion, indicating challenges with administration. • ST-357 (Siga Technologies), a smallpox antiviral with a mechanism of action distinct from tecovirimat and brincidofovir that targets conserved domains in orthopoxviruses, and which is undergoing testing in animal models (Hruby, 2023). • NIOCH-14 is a derivative of tricyclodicarboxylic acid and a pre- cursor of tecovirimat developed and tested in the Russian Federa- tion (ClinicalTrials.gov, 2023; Delaune and Iseni, 2020). In animal models (i.e., an Institute of Cancer Research mouse model and mar- moset model using MPXV challenge), NIOCH-14 demonstrated equal efficacy to tecovirimat and purportedly is easier to produce (Delaune and Iseni, 2020; Mazurkov et al., 2016). • Most recently, a potential for custom designed antivirals for ortho- poxviruses has been demonstrated using CRISPR technologies in in vitro studies (Siegrist et al., 2020) Conclusion on Therapeutics (2-3) To treat smallpox, the following would be advantageous to develop in order to supplement the therapeutic options currently approved and stock- piled in the SNS (1) new, safer antivirals with different and diverse targets, mechanisms of action, and routes of administration that minimize damage to host cells and have a high barrier to the development of resistance; (2) com- bination antiviral treatments and treatments based on novel technologies and platforms (e.g., genome editing, non-conventional targets, etc.); (3) Vaccinia immune globulin intravenous (VIGIV) repurposed as part of combination therapy; (4) diverse options for non-vaccine biologics including monoclonal antibodies and antibody cocktails.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 63 (2-4) Most mpox therapeutics were developed because of investments in small- pox therapeutics, resulting in products found to have activity against mpox. Direct investment in developing therapeutics targeting circulating orthopox- viruses could similarly benefit smallpox therapeutic preparedness and could likely have more immediate utility and potentially achieve commercial viability. OVERARCHING CONCLUSION Based on the evidence and findings on the current state of smallpox MCMs, the committee drew the following overarching conclusion: The COVID-19 pandemic revealed weaknesses in the ability for the nation’s public health and health care systems to rapidly and flexibly adapt the emer- gency response to an unfamiliar pathogen; whereas the 2022 mpox outbreak tested existing MCMs developed primarily for smallpox to contain a less lethal orthopoxvirus. The lessons learned from both emergencies call for strength- ening the nation’s laboratory response systems and further development of point-of-care diagnostics and genomics surveillance capabilities. Additionally, safer, single-dose vaccines and a diverse set of therapeutic options against smallpox would improve the U.S. readiness and response posture for immediate containment and long-term protection in a smallpox emergency. REFERENCES Adams, S. A. 2023. Strategic National Stockpile​smallpox medical countermeasures​overview. Presenta- tion at Meeting 3 of the Committee on Current State of Research, Development, and Stockpiling of Smallpox MCMs of the National Academies. December 14. https://www.nationalacademies. org/event/41411_12-2023_meeting-3-of-the-committee-on-the-current-state-of-research-devel- opment-and-stockpiling-of-smallpox-medical-countermeasures (accessed February 23, 2024). APHL (Association of Public Health Laboratories). 2023. The need for LRN modernization through the lens of an outbreak. https://www.aphl.org/aboutAPHL/publications/lab-matters/Pages/The- Need-for-LRN-Modernization.aspx (accessed March 1, 2024). Ananthula, H. K., S. Parker, E. Touchette, R. M. Buller, G. Patel, D. Kalman, J. S. Salzer, N. Gallardo- Romero, V. Olson, I. K. Damon, T. Moir-Savitz, L. Sallans, M. H. Werner, C. M. Sherwin, and P. B. Desai. 2018. Preclinical pharmacokinetic evaluation to facilitate repurposing of tyrosine kinase inhibitors nilotinib and imatinib as antiviral agents. BMC Pharmacology and Toxicology 19(1):80. Aragón, T. J., S. Ulrich, S. Fernyak, and G. W. Rutherford. 2003. Risks of serious complications and death from smallpox vaccination: A systematic review of the United States experience, 1963–1968. BMC Public Health 3:26. Arness, M. K., R. E. Eckart, S. S. Love, J. E. Atwood, T. S. Wells, R. J. Engler, L. C. Collins, S. L. Lud- wig, J. R. Riddle, and J. D. Grabenstein. 2004. Myopericarditis following smallpox vaccination. American Journal of Epidemiology 160(7):642–651. Baker, R. O., M. Bray, and J. W. Huggins. 2003. Potential antiviral therapeutics for smallpox, monkey- pox and other orthopoxvirus infections. Antiviral Research 57(1–2):13–23. Belongia, E. A., and A. L. Naleway. 2003. Smallpox vaccine: The good, the bad, and the ugly. Clinical Medicine & Research 1(2):87–92. Bhadelia, N. 2015. Rapid diagnostics for Ebola in emergency settings. The Lancet 386(9996):833–835. Bicknell, W. J. 2002. The case for voluntary smallpox vaccination. New England Journal of Medicine 346(17):1323–1325.

64 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Bray, M., and C. J. Roy. 2004. Antiviral prophylaxis of smallpox. Journal of Antimicrobial Chemotherapy 54(1):1–5. Carlin, E. P., N. Giller, and R. Katz. 2017. Estimating the size of the U.S. population at risk of severe adverse events from replicating smallpox vaccine. Public Health Nursing 34(3):200–209. Castillo-Leon, J., R. Trebbien, J. J. Castillo, and W. E. Svendsen. 2021. Commercially available rapid diagnostic tests for the detection of high priority pathogens: Status and challenges. Analyst 146:3750–3776. CDC (U.S. Centers for Disease Control and Prevention). 2016. Negative staining electron microscope protocol for rash illness. https://www.cdc.gov/smallpox/lab-personnel/specimen-collection/neg- ative-stain.html (accessed February 26, 2024). CDC. 2017a. Specimen collection and transport guidelines for suspect smallpox cases. https://www.cdc. gov/smallpox/lab-personnel/specimen-collection/specimen-collection-transport.html (accessed February 6, 2024). CDC. 2017b. Smallpox: For clinicians—Diagnosis & evaluation. https://www.cdc.gov/smallpox/clini- cians/diagnosis-evaluation.html (accessed January 11, 2024). CDC. 2019a. Appendix A: Aventis Pasteur Smallpox Vaccine (APSV). Youtube.com. https://www.you- tube.com/watch?v=wIJU4DXEztA&t=1s (accessed February 23, 2024). CDC. 2019b. Smallpox: Vaccination strategies. https://www.cdc.gov/smallpox/bioterrorism-response- planning/public-health/vaccination-strategies.html (accessed December 22, 2023). CDC. 2022. Smallpox: Vaccines. https://www.cdc.gov/smallpox/clinicians/vaccines.html (accessed January 30, 2024). CDC. 2023a. ACIP recommendations: mpox vaccines. https://www.cdc.gov/vaccines/acip/recommen- dations.html (accessed February 12, 2024). CDC. 2023b. Clinical considerations for treatment and prophylaxis of mpox infection in people who are immunocompromised. https://www.cdc.gov/poxvirus/mpox/clinicians/people-with-HIV.html (accessed March 4, 2024). CDC. 2023c. Clinical treatment. https://www.cdc.gov/poxvirus/mpox/clinicians/treatment.html (ac- cessed February 6, 2024). CDC. 2023d. Guidance for tecovirimat use. https://www.cdc.gov/vaccines/acip/recommendations.html (accessed February 12, 2024). CDC. 2023e. Treatment information for healthcare professionals. https://www.cdc.gov/poxvirus/mpox/ clinicians/treatment.html (accessed February 6, 2024). Chan-Tack, K., P. Harrington, T. Bensman, S. Y. Choi, E. Donaldson, J. O’Rear, D. McMillan, L. Myers, M. Seaton, H. Ghantous, Y. Cao, T. Valappil, D. Birnkrant, and K. Struble. 2021. Benefit–risk assessment for brincidofovir for the treatment of smallpox: U.S. Food and Drug Administration’s evaluation. Antiviral Research 195:105182. CIDRAP (Center for Infectious Disease Research and Policy). 2022. U.S. allows commercial labs to test for monkeypox. https://www.cidrap.umn.edu/us-allows-commercial-labs-test-monkeypox (accessed March 1, 2024). ClinicalTrials.gov. 2023. Study of the safety, tolerability, pharmacokinetics of NIOCH-14 in volunteers aged 18–50 years. https://clinicaltrials.gov/study/NCT05976100 (accessed February 6, 2024). Dalton, A. F., A. O. Diallo, A. N. Chard, D. L. Moulia, N. P. Deputy, A. Fothergill, I. Kracalik, C. W. Wegner, T. M. Markus, P. Pathela, W. L. Still, S. Hawkins, A. T. Mangla, N. Ravi, E. Licherdell, A. Britton, R. Lynfield, M. Sutton, A. P. Hansen, G. S. Betancourt, J. V. Rowlands, S. J. Chai, R. Fisher, P. Danza, M. Farley, J. Zipprich, G. Prahl, K. A. Wendel, L. Niccolai, J. L. Castilho, D. C. Payne, A. C. Cohn, and L. R. Feldstein. 2023. Estimated effectiveness of JYNNEOS vaccine in preventing mpox: A multijurisdictional case–control study—United States, August 19, 2022– March 31, 2023. Morbidity and Mortality Weekly Report 72(20):553–558. Delaune, D., and F. Iseni. 2020. Drug development against smallpox: Present and future. Antimicrobial Agents and Chemotherapy 64(4):e01683-19. DeLaurentis, C. E., J. Kiser, and J. Zucker. 2022. New perspectives on antimicrobial agents: Teco- virimat for treatment of human monkeypox virus. Antimicrobial Agents and Chemotherapy 66(12):e0122622.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 65 Deputy, N. P., J. Deckert, A. N. Chard, N. Sandberg, D. L. Moulia, E. Barkley, A. F. Dalton, C. Sweet, A. C. Cohn, D. R. Little, A. L. Cohen, D. Sandmann, D. C. Payne, J. L. Gerhart, and L. R. Feldstein. 2023. Vaccine effectiveness of JYNNEOS against mpox disease in the United States. New England Journal of Medicine 388(26):2434–2443. Dhillon, R. S., D. Srikrishna, R. F. Garry, and G. Chowell. 2015. Ebola control: Rapid diagnostic testing. The Lancet Infectious Diseases 15(2):147–148. Di Paola, N., M. Sanchez-Lockhart, X. Zeng, J. H. Kuhn, and G. Palacios. 2020. Viral genomics in Ebola virus research. Nature Reviews Microbiology 18(7):365–378. Emergent BioSolutions Canada Inc. 2018. Product monograph including patient medication informa- tion CNJ-016™. https://www.emergentbiosolutions.com/wp-content/uploads/2022/01/VIGIV- Canada-Monograph-English.pdf (accessed February 23, 2024). Engler, R. J., M. R. Nelson, L. C. Collins, Jr., C. Spooner, B. A. Hemann, B. T. Gibbs, J. E. Atwood, R. S. Howard, A. S. Chang, and D. L. Cruser. 2015. A prospective study of the incidence of myocardi- tis/pericarditis and new onset cardiac symptoms following smallpox and influenza vaccination. PLOS One 10(3):e0118283. Fauci, A. S. 2002. Smallpox vaccination policy—the need for dialogue. New England Journal of Medi- cine 346(17):1319–1320. FDA (U.S. Food and Drug Administration). 2021a. JYNNEOS package insert. https://www.fda.gov/ media/131078/download (accessed March 4, 2024). FDA. 2021b. NDA approval–Animal efficacy Tembexa (brincidofovir). Edited by U.S. FDA. https:// www.accessdata.fda.gov/drugsatfda_docs/appletter/2021/214460Origs000,214461Orig1s000ltr. pdf (accessed February 26, 2024). FDA. 2022. ACAM2000 (smallpox vaccine) questions and answers. https://www.fda.gov/vaccines- blood-biologics/vaccines/acam2000-smallpox-vaccine-questions-and-answers (accessed March 3, 2024). FDA. 2023a. Animal rule information. https://www.fda.gov/emergency-preparedness-and-response/ mcm-regulatory-science/animal-rule-information (accessed February 2, 2024). FDA. 2023b. FDA mpox response. https://www.fda.gov/emergency-preparedness-and-response/mcm- issues/fda-mpox-response (accessed February 6, 2024). FDA. 2023c. Monkeypox (mpox) and medical devices. https://www.fda.gov/medical-devices/emer- gency-situations-medical-devices/monkeypox-mpox-and-medical-devices#Laboratories (ac- cessed February 6, 2024). FDA. 2023d. Xpert mpox letter of authorization. https://www.fda.gov/media/165317/download (ac- cessed February 23, 2024). FDA. 2024a. Product classification: Non-variola orthopoxvirus real-time PCR primer and probe set. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=PBK (accessed January 17, 2024). FDA. 2024b. Product classification: Variola virus nucleic acid-based detection assay. https://www.access- data.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=PRA (accessed January 17, 2024). Foege, W. 2011. Lessons and innovations from the West and Central African smallpox eradication program. Vaccine 29(Suppl 4):D10–D12. Foster, S. A., S. Parker, and R. Lanier. 2017. The role of brincidofovir in preparation for a potential smallpox outbreak. Viruses 9(11):320. Frey, S. E., F. K. Newman, J. S. Kennedy, V. Sobek, F. A. Ennis, H. Hill, L. K. Yan, P. Chaplin, J. Vollmar, B. R. Chaitman, and R. B. Belshe. 2007. Clinical and immunologic responses to mul- tiple doses of imvamune (modified vaccinia Ankara) followed by Dryvax challenge. Vaccine 25(51):8562–8573. Freyn, A. W., C. Atyeo, P. L. Earl, J. L. Americo, G. Chuang, H. Natarajan, T. R. Frey, J. G. Gall, J. I. Moliva, R. Hunegnaw, G. A. Arunkumar, C. O. Ogega, A. Nasir, G. Santos, R. H. Levin, A. Meni, P. A. Jorquera, H. Bennet, J. A. Johnson, M. A. Durney, G. Stewart-Jones, J. W. Hooper, T. M. Colpitts, G. Alter, N. J. Sullivan, A. Carfi, and B. Moss. 2023. An mpox virus mRNA-lipid nanoparticle vaccine confers protection against lethal orthopoxviral challenge. Science Transla- tional Medicine 15(716):eadg3540.

66 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Gilchuk, I., P. Gilchuk, G. Sapparapu, R. Lampley, V. Singh, N. Kose, D. L. Blum, L. J. Hughes, P. S. Satheshkumar, M. B. Townsend, A. V. Kondas, Z. Reed, Z. Weiner, V. A. Olson, E. Hammarlund, H. P. Raue, M. K. Slifka, J. C. Slaughter, B. S. Graham, K. M. Edwards, R. J. Eisenberg, G. H. Cohen, S. Joyce, and J. E. Crowe, Jr. 2016. Cross-neutralizing and protective human antibody specificities to poxvirus infections. Cell 167(3):684–694. Gilead Sciences. I. 2000. Vistide® (cidofovir injection). https://www.accessdata.fda.gov/drugsatfda_docs/ label/1999/020638s003lbl.pdf (accessed February 23, 2024). Grosenbach, D. W., R. Jordan, and D. E. Hruby. 2011. Development of the small-molecule antiviral ST-246 as a smallpox therapeutic. Future Virology 6(5):653–671. Grosenbach, D. W., K. Honeychurch, E. A. Rose, J. Chinsangaram, A. Frimm, B. Maiti, C. Lovejoy, I. Meara, P. Long, and D. E. Hruby. 2018. Oral tecovirimat for the treatment of smallpox. New England Journal of Medicine 379(1):44–53. Gruber, M. F., S. Rubin, and P. R. Krause. 2023. Approaches to demonstrating the effectiveness of filovirus vaccines: Lessons from Ebola and COVID-19. Frontiers in Immunology 14:1109486. Hadfield, J., C. Megill, S. M. Bell, J. Huddleston, B. Potter, C. Callender, P. Sagulenko, T. Bedford, and R. A. Neher. 2018. Nextstrain: Real-time tracking of pathogen evolution. Bioinformatics 34(23):4121–4123. Hammarlund, E., M. W. Lewis, S. V. Carter, I. Amanna, S. G. Hansen, L. I. Strelow, S. W. Wong, P. Yoshihara, J. M. Hanifin, and M. K. Slifka. 2005. Multiple diagnostic techniques identify previ- ously vaccinated individuals with protective immunity against monkeypox. Nature Medicine 11(9):1005–1011. Henderson, D. A., and P. Klepac. 2013. Lessons from the eradication of smallpox: An interview with D. A. Henderson. Philosophical Transactions of the Royal Society of London, B: Biological Sciences 368(1623):20130113. HHS (Department of Health and Human Services). 2023. Public Health Emergency Medical Counter- measures Enterprise multiyear budget: Fiscal years 2022–2026. https://aspr.hhs.gov/PHEMCE/ Documents/2022-2026-PHEMCE-Budget.pdf (accessed February 18, 2024). Hou, F., Y. Zhang, X. Liu, Y. M. Murand, J. Xu, Z. Yu, X. Hua, Y. Song, J. Ding, H. Huang, R. Zhao, W. Jia., and X. Yang. 2023. mRNA vaccines encoding fusion proteins of monkeypox virus antigens protect mice from vaccinia virus challenge. Nature Communications 14(5925). Hruby, D. 2023. TPOXX: An orthopox antiviral. Presentation at Meeting 3 of the Committee on Current State of Research, Development, and Stockpiling of Smallpox MCMs of the National Academies. December 14. https://www.nationalacademies.org/event/41411_12-2023_meeting- 3-of-the-committee-on-the-current-state-of-research-development-and-stockpiling-of-small- pox-medical-countermeasures (accessed February 23, 2024). Huston, J., S. Curtis, and E. F. Egelund. 2023. Brincidofovir: A novel agent for the treatment of small- pox. Annals of Pharmacotherapy 57(10):1198–1206. Hutchins, S. S., I. Sulemana, K. L. Heilpern, W. Schaffner, G. Wax, E. B. Lerner, B. Watson, R. Balti- more, R. A. Waltenburg, D. Aronsky, S. Coffin, G. Ng, A. S. Craig, A. Behrman, J. Meek, E. Sher- man, S. S. Chavez, R. Harpaz, and S. Schmid. 2008. Performance of an algorithm for assessing smallpox risk among patients with rashes that may be confused with smallpox. Clinical Infectious Disease 46(Suppl 3):S195–S203. Hutson, C. L., and I. K. Damon. 2010. Monkeypox virus infections in small animal models for evalu- ation of anti-poxvirus agents. Viruses 2(12):2763–2776. IOM (Institute of Medicine). 2002. Scientific and policy considerations in developing smallpox vaccina- tion options: A workshop report. Washington, DC: The National Academies Press. IOM. 2005. The smallpox vaccination program: Public health in an age of terrorism. Washington, DC: The National Academies Press. IOM. 2009. Live variola virus: Considerations for continuing research. Washington, DC: The National Academies Press. IOM and NRC (National Research Council). 2011. BioWatch and public health surveillance: Evaluat- ing systems for the early detection of biological threats: Abbreviated version. Washington, DC: The National Academies Press.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 67 Jordan, R., J. M. Leeds, S. Tyavanagimatt, and D. E. Hruby. 2010. Development of ST-246® for treatment of poxvirus infections. Viruses 2(11):2409–2435. Kaplan, E. H., D. L. Craft, and L. M. Wein. 2002. Emergency response to a smallpox attack: The case for mass vaccination. Proceedings of the National Academy of Sciences 99(16):10935–10940. Karem, K. L., M. Reynolds, Z. Braden, G. Lou, N. Bernard, J. Patton, and I. K. Damon. 2005. Charac- terization of acute-phase humoral immunity to monkeypox: Use of immunoglobulin M enzyme- linked immunosorbent assay for detection of monkeypox infection during the 2003 North American outbreak. Clinical and Diagnostic Laboratory Immunology 12(7):867–872. Kausar, S., F. Said Khan, M. Ishaq Mujeeb Ur Rehman, M. Akram, M. Riaz, G. Rasool, A. Hamid Khan, I. Saleem, S. Shamim, and A. Malik. 2021. A review: Mechanism of action of antiviral drugs. International Journal of Immunopathology and Pharmacology 35:20587384211002621. Kennedy, R. B., and P. A. Gregory. 2023. Chapter 55: Smallpox and vaccinia. In W. Orenstein, P. Offit, K. M. Edwards, and S. Plotkin (eds.), Plotkin’s vaccines (8th edition). Philadelphia: Else- vier. Pp. 1057–1086. Khoury, D. S., T. E. Schlub, D. Cromer, M. Steain, Y. Fong, P. B. Gilbert, K. Subbarao, J. A. Triccas, S. J. Kent, and M. P. Davenport. 2023. Correlates of protection, thresholds of protection, and immunobridging among persons with SARS-CoV-2 infection. Emerging Infectious Diseases 29(2):381–388. Ko, K. K. K., K. R. Chng, and N. Nagarajan. 2022. Metagenomics-enabled microbial surveillance. Nature Microbiology 7(4):486–496. Kost, G. J. 2021. Public health education should include point-of-care testing: Lessons learned from the COVID-19 pandemic. eJIFCC 32(3):311–327. Lane, J. M. 2006. Mass vaccination and surveillance/containment in the eradication of smallpox. Cur- rent Topics in Microbiology Immunology 304:17–29. Lane, J. M., F. L. Ruben, J. M. Neff, and J. D. Millar. 1969. Complications of smallpox vaccination, 1968: National surveillance in the United States. New England Journal of Medicine 281(22):1201–1208. Lane, J. M., F. L. Ruben, J. M. Neff, and J. Millar. 1970. Complications of smallpox vaccination, 1968: Results of ten statewide surveys. The Journal of Infectious Diseases 122(4):303–309. Lewis, R. 2023. Variola virus research: Overview of main activities and use of live virus. Presentation at Meeting 2 of the Committee on Current State of Research, Development, and Stockpiling of Smallpox MCMs of the National Academies. December 1. https://www.nationalacademies. org/event/41410_12-2023_meeting-2-of-the-committee-on-the-current-state-of-research-devel- opment-and-stockpiling-of-smallpox-medical-countermeasures (accessed February 23, 2024). Li, J., I. Hosegood, D. Powell, B. Tscharke, J. Lawler, K. V. Thomas, and J. F. Mueller. 2023. A global aircraft-based wastewater genomic surveillance network for early warning of future pandemics. The Lancet Global Health 11(5):e791–e795. Li, P., J. A. Al-Tawfiq, Z. A. Memish, and Q. Pan. 2023. Preventing drug resistance: Combination treat- ment for mpox. Lancet 402(10414):1750–1751. Li, Y., V. A. Olson, T. Laue, M. T. Laker, and I. K. Damon. 2006. Detection of monkeypox virus with real-time PCR assays. Journal of Clinical Virology 36(3):194–203. Li, Z., A. Sinha, Y. Zhang, N. Tanner, H. T. Cheng, P. Premsrirut, and C. K. S. Carlow. 2023. Extraction- free LAMP assays for generic detection of old world orthopoxviruses and specific detection of mpox virus. Scientific Reports 13(1):21093. Lin, D., Y. Shen, and T. Liang. 2023. Oncolytic virotherapy: Basic principles, recent advances and future directions. Signal Transduction and Targeted Therapy 8(1):156. Mack, T. M., J. Nobel, Jr., and D. B. Thomas. 1972. A prospective study of serum antibody and protec- tion against smallpox. The American Journal of Tropical Medicine and Hygiene 21(2):214–218. Martins, K. 2023. Smallpox therapeutics overview. Presentation at Meeting 3 of the Committee on Current State of Research, Development, and Stockpiling of Smallpox MCMs of the National Academies. December 14. https://www.nationalacademies.org/event/41411_12-2023_meeting- 3-of-the-committee-on-the-current-state-of-research-development-and-stockpiling-of-small- pox-medical-countermeasures (accessed February 23, 2024).

68 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Mazurkov, O. Y., A. S. Kabanov, L. N. Shishkina, A. A. Sergeev, M. O. Skarnovich, N. I. Bormotov, M. A. Skarnovich, A. S. Ovchinnikova, K. A. Titova, D. O. Galahova, L. E. Bulychev, A. A. Sergeev, O. S. Taranov, B. A. Selivanov, A. Y. Tikhonov, E. L. Zavjalov, A. P. Agafonov, and A. N. Sergeev. 2016. New effective chemically synthesized anti-smallpox compound NIOCH-14. Journal of General Virology 97(5):1229–1239. Merchlinsky, M., A. Albright, V. Olson, H. Schiltz, T. Merkeley, C. Hughes, B. Petersen, and M. Chall- berg. 2019. The development and approval of tecoviromat (TPOXX®), the first antiviral against smallpox. Antiviral Research 168:168–174. Meyer, H., R. Ehmann, and G. L. Smith. 2020. Smallpox in the post-eradication era. Viruses 12(2):138. Morgan, J., M. H. Roper, L. Sperling, R. A. Schieber, J. D. Heffelfinger, C. G. Casey, J. W. Miller, S. Santibanez, B. Herwaldt, and P. Hightower. 2008. Myocarditis, pericarditis, and dilated cardiomy- opathy after smallpox vaccination among civilians in the United States, January–October 2003. Clinical Infectious Diseases 46(Suppl3):S242–S250. Moss, B. 2011. Smallpox vaccines: Targets of protective immunity. Immunological Reviews 239(1):8–26. Mucker, E. M., A. J. Goff, J. D. Shamblin, D. W. Grosenbach, I. K. Damon, J. M. Mehal, R. C. Hol- man, D. Carroll, N. Gallardo, V. A. Olson, C. J. Clemmons, P. Hudson, and D. E. Hruby. 2013. Efficacy of tecovirimat (ST-246) in nonhuman primates infected with variola virus (smallpox). Antimicrobial Agents and Chemotherapy 57(12):6246–6253. Murphy, J. G., R. S. Wright, G. K. Bruce, L. M. Baddour, M. A. Farrell, W. D. Edwards, H. Kita, and L. T. Cooper. 2003. Eosinophilic–lymphocytic myocarditis after smallpox vaccination. The Lancet 362(9393):1378–1380. Neff, J. M., J. M. Lane, J. H. Pert, R. Moore, J. D. Millar, and D. A. Henderson. 1967a. Complications of smallpox vaccination: National survey in the United States, 1963. New England Journal of Medicine 276(3):125–132. Neff, J. M., R. H. Levine, J. M. Lane, E. A. Ager, H. Moore, B. J. Rosenstein, J. D. Millar, and D. A. Hen- derson. 1967b. Complications of smallpox vaccination, United States 1963: II. Results obtained by four statewide surveys. Pediatrics 39(6):916–923. NIH (National Institutes of Health). 2022. Decades in the making: mRNA COVID-19 vaccines. https:// covid19.nih.gov/nih-strategic-response-covid-19/decades-making-mrna-covid-19-vaccines (ac- cessed March 4, 2024). Oghuan, J., C. Chavarria, S. R. Vanderwal, A. Gitter, A. A. Ojaruega, C. Monserrat, C. X. Bauer, E. L. Brown, S. J. Cregeen, J. Deegan, B. M. Hanson, M. Tisza, H. I. Ocaranza, J. Balliew, A. W. Maresso, J. Rios, E. Boerwinkle, K. D. Mena, and F. Wu. 2023. Wastewater analysis of mpox virus in a city with low prevalence of mpox disease: An environmental surveillance study. The Lancet Regional Health–Americas 28:100639. Olson, V. A., and S. N. Shchelkunov. 2017. Are we prepared in case of a possible smallpox-like disease emergence? Viruses 9(9):242. https://doi.org/10.3390/v9090242. Orlova, O. V., D. V. Glazkova, E. V. Bogoslovskaya, G. A. Shipulin, and S. M. Yudin. 2022. Develop- ment of modified vaccinia virus Ankara-based vaccines: Advantages and applications. Vaccines (Basel) 10(9):1516. Overton, E. T., J. Stapleton, I. Frank, S. Hassler, P. A. Goepfert, D. Barker, E. Wagner, A. von Krempel- huber, G. Virgin, T. P. Meyer, J. Müller, N. Bädeker, R. Grünert, P. Young, S. Rösch, J. Maclennan, N. Arndtz-Wiedemann, and P. Chaplin. 2015. Safety and immunogenicity of modified vaccinia Ankara-Bavarian Nordic smallpox vaccine in vaccinia-naive and experienced human immu- nodeficiency virus-infected individuals: An open-label, controlled clinical phase II trial. Open Forum Infectious Diseases 2(2):ofv040. Parrino, J., L. H. McCurdy, B. D. Larkin, I. J. Gordon, S. E. Rucker, M. E. Enama, R. A. Koup, M. Ro- ederer, R. T. Bailer, Z. Moodie, L. Gu, L. Yan, and B. S. Graham. 2007. Safety, immunogenicity and efficacy of modified vaccinia Ankara (MVA) against Dryvax challenge in vaccinia-naïve and vaccinia-immune individuals. Vaccine 25(8):1513–1525.

SMALLPOX MEDICAL COUNTERMEASURES READINESS 69 Peiró-Mestres, A., I. Fuertes, D. Camprubí-Ferrer, M. Marcos, A. Vilella, M. Navarro, L. Rodriguez- Elena, J. Riera, A. Català, M. J. Martínez, and J. L. Blanco. 2022. Frequent detection of monkey- pox virus DNA in saliva, semen, and other clinical samples from 12 patients, Barcelona, Spain, May to June 2022. Euro Surveillance 27(28):2200503. Petersen, B. W., I. K. Damon, C. A. Pertowski, D. Meaney-Delman, J. T. Guarnizo, R. H. Beigi, K. M. Edwards, M. C. Fisher, S. E. Frey, R. Lynfield, and R. E. Willoughby. 2015. Clinical guidance for smallpox vaccine use in a postevent vaccination program. Morbidity and Mortality Weekly Report Recommendations and Reports 64(2):1–32. Phetsouphanh, C., D. R. Darley, D. B. Wilson, A. Howe, C. M. L. Munier, S. K. Patel, J. A. Juno, L. M. Burrell, S. J. Kent, G. J. Dore, A. D. Kelleher, and G. V. Matthews. 2022. Immunological dysfunc- tion persists for 8 months following initial mild-to-moderate SARS-CoV-2 infection. Nature Immunology 23(2):210–216. Pinnetti, C., E. Cimini, V. Mazzotta, G. Matusali, A. Vergori, A. Mondi, M. Rueca, S. Batzella, E. Tartaglia, A. Bettini, S. Notari, M. Rubino, M. Tempestilli, C. Pareo, L. Falasca, F. Del Nonno, A. Scarabello, M. Camici, R. Gagliardini, E. Girardi, F. Vaia, F. Maggi, C. Agrati, and A. Antinori. 2023. Mpox as AIDS-defining event with a severe and protracted course: Clinical, immunologi- cal, and virological implications. The Lancet Infectious Diseases 24(2):e127–e135. Pittman, P. R., M. Hahn, H. S. Lee, C. Koca, N. Samy, D. Schmidt, J. Hornung, H. Weidenthaler, C. R. Heery, T. P. H. Meyer, G. Silbernagl, J. Maclennan, and P. Chaplin. 2019. Phase 3 efficacy trial of modified vaccinia Ankara as a vaccine against smallpox. New England Journal of Medicine 381(20):1897–1908. https://doi.org/10.1056/NEJMoa1817307. Ratner, L. H., J. M. Lane, and C. N. Vicéns. 1970. Complications of smallpox vaccination: Surveillance during an island-wide program in Puerto Rico, 1967–1968. American Journal of Epidemiology 91(3):278–285. Reeves, P. M., B. Bommarius, S. Lebeis, S. McNulty, J. Christensen, A. Swimm, A. Chahroudi, R. Cha- van, M. B. Feinberg, D. Veach, W. Bornmann, M. Sherman, and D. Kalman. 2005. Disabling pox- virus pathogenesis by inhibition of Abl-family tyrosine kinases. Nature Medicine 11(7):731–739. Reeves, P. M., S. K. Smith, V. A. Olson, S. H. Thorne, W. Bornmann, I. K. Damon, and D. Kalman. 2011. Variola and monkeypox viruses utilize conserved mechanisms of virion motility and release that depend on Abl and SRC family tyrosine kinases. Journal of Virology 85(1):21–31. Ristanovic, E., A. Gligic, S. Atanasievska, V. Protic-Djokic, D. Jovanovic, and M. Radunovic. 2016. Smallpox as an actual biothreat: Lessons learned from its outbreak in ex-Yugoslavia in 1972. Annali dell’Istituto Superiore di Sanita 52(4):587–597. Rogers, J. H., K. Newell, B. Westley, and J. Laurence. 2024. Fatal Alaskapox infection in a southcentral Alaska resident. State of Alaska Epidemiology Bulletin, February 9. https://epi.alaska.gov/bul- letins/docs/b2024_02.pdf (accessed February 22, 2024). Rosenberg, E. S., V. Dorabawila, R. Hart-Malloy, B. J. Anderson, W. Miranda, T. O’Donnell, C. J. Gonzalez, M. Abrego, C. DelBarba, C. J. Tice, C. McGarry, E. C. Mitchell, M. Boulais, B. Backenson, M. Kharfen, J. McDonald, and U. E. Bauer. 2023. Effectiveness of JYNNEOS vaccine against diagnosed mpox infection—New York, 2022. Morbidity and Mortality Weekly Report 72(20):559–563. Russo, A. T., D. W. Grosenbach, T. L. Brasel, R. O. Baker, A. G. Cawthon, E. Reynolds, T. Bailey, P. J. Kuehl, V. Sugita, K. Agans, and D. E. Hruby. 2018. Effects of treatment delay on efficacy of tecovirimat following lethal aerosol monkeypox virus challenge in cynomolgus macaques. The Journal of Infectious Diseases 218(9):1490–1499. Russo, A. T., A. Berhanu, C. B. Bigger, J. Prigge, P. M. Silvera, D. W. Grosenbach, and D. Hruby. 2020. Co-administration of tecovirimat and ACAM2000™ in non-human primates: Effect of teco- virimat treatment on ACAM2000 immunogenicity and efficacy versus lethal monkeypox virus challenge. Vaccine 38(3):644–654. Ryan, M. A. K., J. F. Seward, and Smallpox Vaccine in Pregnancy Registry Team. 2008. Pregnancy, birth, and infant health outcomes from the national smallpox vaccine in pregnancy registry, 2003–2006. Clinical Infectious Diseases 46(Suppl 3):S221–S226.

70 FUTURE STATE OF SMALLPOX MEDICAL COUNTERMEASURES Sah, R., A. Abdelaal, A. Asija, S. Basnyat, Y. R. Sedhai, S. Ghimire, S. Sah, D. K. Bonilla-Aldana, and A. J. Rodriguez-Morales. 2022. Monkeypox virus containment: The application of ring vaccination and possible challenges. Journal of Travel Medicine 29(6):taac085. Saravanan, K. A., M. Panigrahi, H. Kumar, D. Rajawat, S. S. Nayak, B. Bhushan, and T. Dutt. 2022. Role of genomics in combating COVID-19 pandemic. Gene 823:146387. Sarkar, J. K., A. C. Mitra, M. K. Mukherjee, S. K. De, and D. G. Mazumdar. 1973. Virus excretion in smallpox. 1. Excretion in the throat, urine, and conjunctiva of patients. Bulletin of the World Health Organization 48(5):517–522. Seaman, M. S., M. B. Wilck, L. R. Baden, S. R. Walsh, L. E. Grandpre, C. Devoy, A. Giri, L. C. Noble, J. A. Kleinjan, K. E. Stevenson, H. T. Kim, and R. Dolin. 2010. Effect of vaccination with modi- fied vaccinia Ankara (ACAM3000) on subsequent challenge with Dryvax. Journal of Infectious Diseases 201(9):1353–1360. Sharma, S., J. Pannu, S. Chorlton, J. L. Swett, and D. J. Ecker. 2023. Threat Net: A metagenomic surveil- lance network for biothreat detection and early warning. Health Security 21(5)347–357. Siegrist, C. M., S. M. Kinahan, T. Settecerri, A. C. Greene, and J. L. Santarpia. 2020. CRISPR/Cas9 as an antiviral against orthopoxviruses using an AAV vector. Scientific Reports 10(1)19307. Siegrist, E. A., and J. Sassine. 2023. Antivirals with activity against mpox: A clinically oriented review. Clinical Infectious Diseases 76(1):155–164. Skiest, D. J., M. Duong, S. Park, L. Wei, and P. Keiser. 1999. Complications of therapy with intrave- nous cidofovir: Severe nephrotoxicity and anterior uveitis. Infectious Diseases in Clinical Practice 8(3):151–157. Smith, T. G., C. M. Gigante, N. T. Wynn, A. Matheny, W. Davidson, Y. Yang, R. E. Condori, K. O’Connell, L. Kovar, T. L. Williams, Y. C. Yu, B. W. Petersen, N. Baird, D. Lowe, Y. Li, P. S. Satheshkumar, and C. L. Hutson. 2023. Tecovirimat resistance in mpox patients, United States, 2022–2023. Emerging Infectious Diseases 29(12):2426–2432. Suthar, A. B., S. Schubert, J. Garon, A. Couture, A. M. Brown, and S. Charania. 2022. Coronavirus disease case definitions, diagnostic testing criteria, and surveillance in 25 countries with highest reported case counts. Emerging Infectious Diseases 28(1):148–156. Tack, D. M., K. L. Karem, J. R. Montgomery, L. Collins, M. G. Bryant-Genevier, R. Tiernan, M. Cano, P. Lewis, R. J. Engler, I. K. Damon, and M. G. Reynolds. 2013. Unintentional transfer of vaccinia virus associated with smallpox vaccines: ACAM2000® compared with Dryvax®. Human Vaccines & Immunotherapeutics 9(7):1489–1496. Taub, D. D., W. B. Ershler, M. Janowski, A. Artz, M. L. Key, J. McKelvey, D. Muller, B. Moss, L. Fer- rucci, P. L. Duffey, and D. L. Longo. 2008. Immunity from smallpox vaccine persists for decades: A longitudinal study. American Journal of Medicine 121(12):1058–1064. Ulaeto, D. O., S. G. Lonsdale, S. M. Laidlaw, G. C. Clark, P. Horby, and M. W. Carroll. 2022. A prototype lateral flow assay for detection of orthopoxviruses. Lancet Infectious Diseases 22(9):1279–1280. WHO (World Health Organization). 2023. Meeting of the Strategic Advisory Group of Experts on Immunization, September 2023: Conclusions and recommendations. Weekly Epidemiologi- cal Record 47:599–620. https://iris.who.int/bitstream/handle/10665/374327/WER9847-eng-fre. pdf?sequence=1 (accessed February 23, 2024). WHO. 2024. 154th session of the executive board, provisional agenda item 18—Smallpox eradication: Destruction of variola virus stocks (January 2, 2024). https://apps.who.int/gb/ebwha/pdf_files/ EB154/B154_20-en.pdf (accessed February 23, 2024). Wolfe, D. 2023. Smallpox vaccines overview. Presentation at Meeting 3 of the Committee on Current State of Research, Development, and Stockpiling of Smallpox MCMs of the National Academies. December 14. https://www.nationalacademies.org/event/41411_12-2023_meeting-3-of-the- committee-on-the-current-state-of-research-development-and-stockpiling-of-smallpox-medi- cal-countermeasures (accessed February 23, 2024).

SMALLPOX MEDICAL COUNTERMEASURES READINESS 71 Yang, G., D. C. Pevear, M. H. Davies, M. S. Collett, T. Bailey, S. Rippen, L. Barone, C. Burns, G. Rhodes, S. Tohan, J. W. Huggins, R. O. Baker, R. L. Buller, E. Touchette, K. Waller, J. Schriewer, J. Neyts, E. DeClercq, K. Jones, D. Hruby, and R. Jordan. 2005. An orally bioavailable antipox- virus compound (ST-246) inhibits extracellular virus formation and protects mice from lethal orthopoxvirus challenge. Journal of Virology 79(20):13139–13149. Zitzmann-Roth, E. M., F. Von Sonnenburg, S. De La Motte, N. Arndtz-Wiedemann, A. Von Krem- pelhuber, N. Uebler, J. Vollmar, G. Virgin, and P. Chaplin. 2015. Cardiac safety of modified vaccinia Ankara for vaccination against smallpox in a young, healthy study population. PLOS One 10(4):e0122653.

Next: 3 Factors Influencing Smallpox Readiness and Response »
Future State of Smallpox Medical Countermeasures Get This Book
×
 Future State of Smallpox Medical Countermeasures
Buy Paperback | $23.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

At the request of the Administration for Strategic Preparedness and Response, the National Academies convened a committee to examine lessons learned from the COVID-19 pandemic and mpox multi-country outbreak to inform an evaluation of the state of smallpox research, development, and stockpiling of medical countermeasures (MCM). In the resulting report, the committee presents findings and conclusions that may inform U.S. Government investment decisions in smallpox MCM readiness, as well as the official U.S. position on the disposition of live viral collections at future World Health Assembly meetings.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!