Rapid Expert Consultation on SARS-CoV-2 Surface Stability and Incubation for the COVID-19 Pandemic (March 15, 2020)
March 15, 2020
Kelvin Droegemeier, Ph.D.
Office of Science and Technology Policy
Executive Office of the President
Eisenhower Executive Office Building
1650 Pennsylvania Avenue, NW
Washington, DC 20504
Dear Dr. Droegemeier:
You requested immediate feedback on two crucial questions. The following expert members of the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats were involved in preparing this document: Kent Kester, David Relman, David Walt, and me. Ellen Wright Clayton, Vanderbilt University, reviewed this document.
Question 1: Survival of virus on surfaces.
One of the most thorough and informative studies is just now under consideration for publication and has not undergone full peer review. The investigators are a highly reputable group, and we can expect that their study was carefully conducted. They tested both the current coronavirus (SARS-CoV-2) and the original SARS virus (SARS-CoV-1). Results were similar for both viruses. They tested the viability (survival) of both viruses after controlled aerosolization and on a variety of surfaces. The aerosol (particles smaller than 5 microns that can float in the air) showed viral detection up to 3 hours post aerosolization. Following surface contamination, SARS-CoV-2 could be detected up to 4 hours on copper, up to 24 hours on cardboard and up to 2-3 days on plastic and on stainless steel. These results are consistent with the plausibility of both aerosol and surface (fomite) transmission of SARS-CoV2. The difference in survival on copper (4 hours) and on stainless steel (2-3 days) is noteworthy. Note that this study excludes what is probably the most common route of spread, direct droplet transmission by cough or sneeze, or even exhalation by an infected person. Additionally, the members of the standing committee identified above note that the National Biodefense Analysis and Countermeasures Center (NBACC) is conducting environmental survival studies of SARSCoV-2 and their results should be taken into account.
Question 2: Incubation period (time between exposure and onset of symptoms).
Note that it is possible for viral shedding to begin prior to the onset of symptoms. Also, we are not considering here the question of how long viral shedding can continue in someone who has been infected.
Rather, as we understand it, the question here pertains to the appropriate period of quarantine for an exposed individual. One of the more informative reports on incubation period studied 181 patients in China who had identifiable dates of exposure and of symptom onset.1 In this study, the mean incubation period was estimated to be 5.1 days (95% confidence interval 4.5 to 5.8 days) and 97.5% of those who develop symptoms will do so within 11.5 days (95% confidence interval 8.2 to 15.6 days) of exposure. These estimates imply that only about 1% of cases (101/10,000) will develop symptoms following 14 days after exposure. Shortening quarantine to fewer than 14 days would increase the fraction who were still to develop symptoms. Note that Lauer et al. acknowledged that publicly reported cases may overrepresent severe cases, the incubation period for which may differ from that of mild cases.
Harvey V. Fineberg, M.D., Ph.D.
Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats
This activity was supported by a contract between the National Academy of Sciences and the U.S. Department of Health and Human Services’ Office of the Assistant Secretary for Preparedness and Response (75A50120C00093). Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.
Copyright 2020 by the National Academy of Sciences. All rights reserved.
1 Lauer et al. 2020. The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: Estimation and application free. Annals of Internal Medicine. DOI: 10.7326/M20-0504.