Persons infected with coronavirus may be symptom-free for 5 days
Estimated incubation period supports current CDC recommendations for active monitoring
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Evidence suggests that persons infected with SARS-CoV-2, the newly-identified virus that causes coronavirus disease COVID-19, may be symptom-free for about 5 days on average, and should expect to experience symptoms within 12 days. These findings, published in Annals of Internal Medicine, support current recommendations by the US Centers for Disease Control and Prevention (CDC) to actively monitor patients for 14 days after an assumed exposure to SARS-CoV-2 and have important implications for informing control activities.
In December 2019, a cluster of severe pneumonia cases of unknown etiology was reported in Wuhan, Hubei province, China. These cases were soon attributed to a novel strain of coronavirus belonging to the same family of viruses causing Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and the four human coronaviruses associated with the common cold. Infection with the virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can be asymptomatic or result in mild to severe symptomatic disease (coronavirus disease 2019, or COVID-19). Current understanding of the incubation period for COVID-19 is limited.
Researchers from Johns Hopkins Bloomberg School of Public Health conducted an analysis of news reports, public health reports, and press releases from 50 provinces, regions, and countries outside of Wuhan, China to estimate the length of the incubation period of COVID-19, the time from exposure to symptom onset. They found information on 181 confirmed cases with identifiable exposure and symptom onset windows. Based on the available data, the researchers estimated the median incubation period of COVID-19 to be 5.1 days and 97.5 percent of those who develop symptoms appeared to do so within 11.5 days of infection. These estimates imply that, under conservative assumptions, 101 out of every 10,000 cases will develop symptoms after 14 days of active monitoring or quarantine, which supports current CDC recommendations.
The authors caution that given recent evidence of SARS-CoV-2 transmission by mildly symptomatic and asymptomatic individuals, time from exposure to onset of infectiousness (latent period) may be shorter than the estimated incubation period, with important implications for transmission dynamics.