By GSN Staff

An analysis of publicly available data on infections from SARS-CoV-2 estimates 5.1 days as the median incubation period for COVID-19, according to researchers at the Johns Hopkins Bloomberg School of Public Health.

About 97.5% of people who develop symptoms of COVID-19 will do so within 11.5 days of exposure. The researchers estimated that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine (Ann Intern Medbbacetuqracadeawrtacdy 2019 Mar 9. [Epub ahead of print]).


For the study, the researchers analyzed 181 cases from China and other countries that were detected prior to Feb. 24, were reported in the media, and included likely dates of exposure and symptom onset. Most of the cases involved travel to or from Wuhan, China, the epicenter of the pandemic, or exposure to individuals who had been to Hubei Province, where Wuhan is located.

The CDC has been recommending a 14-day quarantine or active monitoring period for individuals who are known to be at high risk for infection due to contact with known cases or travel to a heavily affected area.

“Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although with that period some cases would be missed over the long term,” said study senior author Justin Lessler, PhD, an associate professor in the Bloomberg School’s Department of Epidemiology, in Baltimore.


The global COVID-19 pandemic began in December 2019 in Wuhan, and has resulted in 125,048 officially confirmed cases globally and 4,613 deaths from pneumonia caused by the virus, according to the World Health Organization’s March 12 situation report. Most of the cases are still from China, South Korea and Italy, but more than 117 countries have reported cases, including the United States. 

An accurate estimate of the incubation period for a new virus makes it easier for epidemiologists to gauge the likely dynamics of the outbreak, and allows public health officials to design effective quarantine and other control measures, the researchers said. Quarantines typically slow the spread of infection, even if there are some outlier cases with incubation periods that exceed the quarantine period. (China reported 26 new cases on March 12, compared with 1,985 on Jan. 26.)

The new estimate of 5.1 days for the median incubation period of SARS-CoV-2 is similar to estimates from the earliest studies of this new virus, which were based on fewer cases. This incubation period for SARS-CoV-2 is in the same range as SARS-CoV, the coronavirus that caused SARS in southern China and Hong Kong from 2002 to 2004. For MERS-CoV, which caused hundreds of MERS cases in the Middle East, with a relatively high fatality rate, the estimated mean incubation period is five to seven days.

Human coronaviruses that cause common colds have mean disease incubation periods of about three days, the researchers said.