• Stephen A Lauer, Kyra H Grantz, Qifang Bi, Forrest K Jones, Qulu Zheng, Hannah R Meredith, Andrew S Azman, Nicholas G Reich, and Justin Lessler.
• Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland (S.A.L., K.H.G., Q.B., F.K.J., Q.Z., H.R.M., A.S.A., J.L.).
• Ann. Intern. Med. 2020 May 5; 172 (9): 577582577-582.

BackgroundA novel human coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was identified in China in December 2019. There is limited support for many of its key epidemiologic features, including the incubation period for clinical disease (coronavirus disease 2019 [COVID-19]), which has important implications for surveillance and control activities.ObjectiveTo estimate the length of the incubation period of COVID-19 and describe its public health implications.DesignPooled analysis of confirmed COVID-19 cases reported between 4 January 2020 and 24 February 2020.SettingNews reports and press releases from 50 provinces, regions, and countries outside Wuhan, Hubei province, China.ParticipantsPersons with confirmed SARS-CoV-2 infection outside Hubei province, China.MeasurementsPatient demographic characteristics and dates and times of possible exposure, symptom onset, fever onset, and hospitalization.ResultsThere were 181 confirmed cases with identifiable exposure and symptom onset windows to estimate the incubation period of COVID-19. The median incubation period was estimated to be 5.1 days (95% CI, 4.5 to 5.8 days), and 97.5% of those who develop symptoms will do so within 11.5 days (CI, 8.2 to 15.6 days) of infection. These estimates imply that, under conservative assumptions, 101 out of every 10 000 cases (99th percentile, 482) will develop symptoms after 14 days of active monitoring or quarantine.LimitationPublicly reported cases may overrepresent severe cases, the incubation period for which may differ from that of mild cases.ConclusionThis work provides additional evidence for a median incubation period for COVID-19 of approximately 5 days, similar to SARS. Our results support current proposals for the length of quarantine or active monitoring of persons potentially exposed to SARS-CoV-2, although longer monitoring periods might be justified in extreme cases.Primary Funding SourceU.S. Centers for Disease Control and Prevention, National Institute of Allergy and Infectious Diseases, National Institute of General Medical Sciences, and Alexander von Humboldt Foundation.

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