Coronavirus: If you have the infection, it could be 5.1 days before symptoms start showing, says new estimate
If a person has the new coronavirus infection, they will start showing symptoms about 5.1 days after becoming infected, according to a new estimate.
The study -- led by researchers at Johns Hopkins Bloomberg School of Public Health -- also suggests that about 97.5% of people who develop symptoms of COVID-19 infection will do so within 11.5 days of exposure.
“An analysis of publicly available data on infections from the new coronavirus that causes the respiratory illness COVID-19 yielded an estimate of 5.1 days for the median disease incubation period,” says the study published in the Annals of Internal Medicine.
According to experts, understanding this incubation period -- that is, is the time between catching the virus and showing symptoms of disease -- is critical for health authorities. It allows them to introduce more effective quarantine systems for people suspected of carrying the virus, as a way of controlling and hopefully preventing the spread of the virus. Globally, the new coronavirus has so far killed 3,825, and infected around 110,000 in over 100 countries, show current estimates.
“An accurate estimate of the disease 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. Quarantines typically slow and may ultimately stop the spread of infection, even if there are some outlier cases with incubation periods that exceed the quarantine period,” says the study.
The incubation period for the novel coronavirus has been estimated at 2 to 14 days by the US Centers for Disease Control and Prevention (CDC). The CDC and many other public health authorities around the world have been using a 14-day quarantine or active-monitoring period for individuals who are known to be at high risk of infection due to contact with known cases or travel to a heavily affected area.
Based on their findings, the experts say that this median time of 5.1 days from exposure to onset of symptoms suggests that the 14-day quarantine period used by the CDC and other countries for individuals with likely exposure to the coronavirus is reasonable.
“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," says study senior author Justin Lessler, an associate professor in the Bloomberg School's Department of Epidemiology, in the analysis.
For the study, the researchers analyzed 181 cases from China and other countries that were detected before February 24, and 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 city at the center of the epidemic, or exposure to individuals who had been to Hubei, the province for which Wuhan is the capital.
The researchers estimated that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine. The symptoms that may appear 2-14 days after exposure include fever, cough, and shortness of breath.
The new estimate of 5.1 days for the median incubation period of COVID-19 is similar to estimates from the earliest studies of this new virus, which were based on fewer cases. The research team says that this incubation period is also in the same range as Severe Acute Respiratory Syndrome coronavirus or SARS-CoV, a different human-infecting coronavirus. For Middle East respiratory syndrome coronavirus (MERS-CoV), the estimated mean incubation period is 5-7 days, they add.
“Human coronaviruses that cause common colds have mean illness-incubation periods of about three days,” says the study.