Modeling Community Containment for Pandemic Influenza A Letter Report (2006) / Chapter Skim
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Letter Report
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Agwunobi: On behalf of the Institute of Medicine (IOM) Committee on Modeling Community Containment for Pandemic Influenza, I am pleased to report our conclusions and recommendations.
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All these uncertainties are magnified when considering pandemic influenza. Three previous pandemics occurred during the 20th century.3 The 1918-1919 pandemic (often referred to as the "Spanish influenza")
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This report reviews models that were specifically developed to assess potential community containment strategies of pandemic influenza. First an overview of models and their role in policy decisions is presented.
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. Model-based analyses have appeared with growing frequency in the infectious diseases literature.
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and, to a lesser extent, room ventilation, humidifiers, and social distancing in reducing transmission. His find 5The committee was aware that the MIDAS modelers were specifically commissioned to prepare models that could inform federal policymaking.
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in mitigating a pandemic influenza outbreak in the United States. TLC includes a combination of interventions that includes: targeted antiviral treatment and isolation of ascertained cases, targeted prophylaxis and quarantine of household contacts of index cases, school closure and keeping children at home for the duration of the closure; social distancing in workplace (e.g., via telecommuting)
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, which was not part of the MIDAS group but which did focus on many of the TLC interventions, assumed a high degree of transmission in schools and among children and therefore predicts that school closure is an extremely important intervention and that using it alone can substantially reduce overall attack rates (Glass et al., 2006a,b)
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. Specific interventions examined include: school closure, child/teen social distancing, adult and senior social distancing, home quarantine, targeted antiviral treatment for diagnosed individuals, antiviral prophylaxis of household members, and extended antiviral prophylaxis of persons linked through house, school, work, and neighborhood contact.
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For example, the model assumes that all mitigation strategies begin after 10 individuals are diagnosed within the community, that adults are able to stay home to care for the sick or watch children following school closure, and that there is high compliance with interventions (90 percent)
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Rather than providing a critique of each model, the committee comments on the general strengths and limitations of the state of modeling for pandemic influenza and areas where models could be improved to aid policymakers. In terms of strengths, the committee found that the models were useful in organizing the current state of knowledge about potential responses to influenza pandemic.
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Observational or randomized studies should also be undertaken to evaluate the effectiveness of certain interventions in commu nity settings. Results of these studies should be incorporated into the various models of pandemic influenza as appropriate.
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Because of the significant constraints placed on the models, it is not surprising that the results of the three models were similar. Other types of models have been developed that could inform policy on pandemic influenza and 9See section below in "Historical Analyses" on modeling of French seasonal influenza surveillance data by Ferguson and colleagues for an example of current efforts to evaluate the effectiveness of school closures.
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Increased public dialogue among policymakers, modelers, and stakeholders is also necessary for improving the models. Recommendation 6: The committee recommends that policymakers regularly convene forums for public dialogue on pandemic influenza modeling and analyses, and recommends the development of a standing expert panel to pro vide ongoing advice regarding models of pandemic influenza.
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In addition, existing data on influenza should be compiled, inte grated, and made publicly available, and updated in a timely way so that it is available to more of the modeling community. Other strategies that could improve the predictive ability of models of pandemic influenza include the following: · Current simulation models of pandemic influenza need to be further developed and validated.
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He also observed that "fatigue" was an important factor; in other words, communities which had to reinstitute interventions after having lifted them experienced pushback and noncompliance in the second phase of restrictions. Finally, he concluded that the community interventions may have lowered the peak death rate and that proactive and early implementation were associated with flatter epidemic curves, although there were examples of cities that implemented the strategies but still had severe epidemics.
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The second analysis uses seasonal influenza data from France to estimate the importance of school-based transmission in propagating seasonal influenza epidemics and the likely impact of school closure on transmission of influenza during a pandemic. The first analysis is based on two observations about the 1918 pandemic.
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They first modeled what the epidemic curve in each city would have looked like had there been no interventions. Then they modeled the epidemic curve in each city if assuming in addition to no interventions, there was also no spontaneous social distancing.
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(2006) ; that is, school closure would cause only a small reduction on overall attack rates, but that it would have a significant impact on peak rates.
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LESSONS FROM SIMULATION MODELS AND HISTORICAL ANALYSES Several lessons can be gleaned from the simulation models and historical analyses. The models generally suggest that a combination of targeted antivirals and NPIs can delay and flatten the epidemic peak, but the evidence is less convincing that they can reduce the overall size of the epidemic.
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Some of the evidence is generally derived from other respiratory illnesses. THE ROLE FOR AND COMMUNITY IMPACT OF CONTAINMENT STRATEGIES The committee's task was to review the evidence supporting community-wide interventions for pandemic influenza.
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, use of antiviral drugs is prominent in many of the descriptions of possible interventions that could be used to contain a community-wide outbreak of pandemic influenza. Antiviral treatment or prophylaxis is also considered in some of the computational models developed to study community containment.
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Recommendation 8: The committee recommends that future assessments of nonpharmaceutical interventions for pandemic influenza include considera tion of both their potential public health benefits as well as their potential
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The RAND model, while preliminary as described above, included hand hygiene, respiratory etiquette, rapid diagnosis, and surveillance in their "expert choice" intervention, which the model predicts will have utility in mitigating virus transmission in com 14On the other hand, the committee recognizes the potential value of implementing public health interventions that are not strongly based on evidence of effectiveness. A benefit of an intervention could be that government action, whether or not based on scientific evidence, can promote civil order and public trust.
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for influenza calls into question the relevance of the experience with mask use by the general public during SARS. Conclusion 1: In summary, evidence suggests a role for surveillance and case reporting, rapid viral diagnosis, hand hygiene, and respiratory etiquette in re ducing pandemic influenza virus transmission.
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Conclusion 2: In summary, evidence suggests a role for antiviral prophylaxis and treatment in reducing pandemic influenza virus transmission within households and healthcare settings. Use of these drugs during a pandemic will require monitoring of resistance to the drugs and appropriate modification of this strategy if resistance emerges.
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Provision of social support is thought to increase adherence to isolation and some social distancing recommendations and therefore to increase the effectiveness of those measures. The CDC recommends that sick individuals suffering from respiratory illnesses including seasonal influenza stay home from work, school, and social gatherings (http://www.cdc.gov/flu/symptoms.htm)
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to allow for individual action by the contact, voluntary sheltering, and quarantine in reducing pandemic influenza virus transmission. The evidence derives from modeling and expert opinion.
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Conclusion 5: In summary, the evidence suggests a role for community restric tions in reducing pandemic influenza virus transmission. The evidence does not allow for differentiating possible effects of specific types of community re strictions, nor does it allow differentiation between voluntary versus manda tory community restrictions.
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, and countless exercises in emergency management, public health, and disaster preparedness all endorse a role for a key spokesperson during a crisis such as pandemic influenza. Conclusion 6: In summary, the evidence suggests a critically important role for risk communication, specifically the identification of key and trusted spokespersons, in cultivating an environment conducive to public acceptance of and adherence to community containment strategies for reducing pandemic influenza virus transmission.
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Sincerely, Adel Mahmoud, M.D., Ph.D. On behalf of the Committee on Modeling Community Containment for Pandemic Influenza
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The committee was unable to prioritize or otherwise distinguish among the individual community interventions. 24Rapid viral diagnosis would be important during the early phase of a pandemic but unfeasible and unnecessary in the late phases.
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differentiating possible adverse · The committee identified effects of specific types of "intervention-fatigue" as a community restrictions, nor does factor that could under it allow differentiation between mine the potential effec voluntary versus mandatory tiveness of any of these community restrictions measures. · In general, evidence from mod eling and from historical analy ses suggests that early interven tion shows more promise than later intervention · The main effect might be to slow the time to peak of the outbreak in a community, which could be important for hospital-based management of ill patients and to allow for delivery of vaccine if available Risk Communication · Identification of key and trusted Effective risk communica spokespersons to cultivate an tion will increase the likeli environment conducive to public hood that recommended acceptance of and adherence to community interventions community containment strate- are: gies · understood, · adhered to, and · maximally effective.
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In addition, existing data on influenza should be compiled, integrated, and made publicly available, and updated in a timely way so that it is available to more of the modeling community. Recommendation 8: The committee recommends that future assessments of nonpharmaceutical interventions for pandemic influenza include consideration of both their potential public health benefits as well as their potential negative effects.
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Key accompaniments to the policy guidance include a communication plan, plans for when to trigger the interventions and when to rescind them, and plans to help mitigate the adverse consequences of implementing some of the policies. Recommendation 11: The committee recommends that any discussion of using these interventions consider not only their potential health benefits, but also their likely ethical, social, economic, and logistical costs.
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PowerPoint presentation at the Workshop on Modeling Community Containment of the Institute of Medicine Committee on the role of Community-Based Mitigation Strategies During a Pandemic Influenza. Washington DC.
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PowerPoint presentation at the Institute of Medicine Workshop on Modeling Community Containment, Washington DC. Insti tute of Medicine Committee on Modeling Community Containment of an Influenza Pandemic.
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