Researchers at Johns Hopkins Bloomberg School of Public Health estimate that SARS-CoV-2 (the coronavirus that causes COVID-19) has a median disease incubation period of 5.1 days.

For the study, the researchers analyzed 181 cases from China and other countries that were detected prior to February 24. The new estimate of 5.1 days for the median incubation period of SARS-CoV-2 is similar to estimates from the earliest studies, which had smaller data samples.

According to data, about 97.5% of people who develop COVID-19 symptoms will do so within 11.5 days of exposure, a figure that supports the CDC’s established 14-day quarantine period for persons exposed to or potentially exposed to the virus, researchers wrote.

In fact, data suggested that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine, or 1.01%.

“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, an associate professor in the Bloomberg School’s Department of Epidemiology.

Researchers also compared the mean incubation period to other known coronaviruses and reported:

  • SARS-CoV-1 (which causes SARS) had a similar incubation period to SARS-CoV-2
  • MERS-CoV, (which causes Middle East Respiratory Syndrome) has a mean incubation period of 5-7 days, but a much higher fatality rate.
  • Human coronaviruses that cause common colds have mean illness-incubation periods of about 3 days.

Lessler and colleagues have also published an online tool that allows public health officials and members of the public to estimate how many cases would be caught and missed under different quarantine periods.

Photo credit: NIAID-RML. Novel Coronavirus SARS-CoV-2. This scanning electron microscope image shows SARS-CoV-2 (round gold objects) emerging from the surface of cells cultured in the lab. SARS-CoV-2, also known as 2019-nCoV, is the virus that causes COVID-19. The virus shown was isolated from a patient in the US.