It takes five days for coronavirus symptoms to appear


According to a new study led by researchers at Johns Hopkins University, analysis of publicly available data on infections with the new coronavirus, SARS-CoV-2, which causes the respiratory disease COVID-19 has concluded with an estimate of 5.1 days for the average incubation period of the disease. This median time from exposure to onset of symptoms suggests that the 14-day quarantine period used by the Centers for Disease Control and Prevention for people with probable exposure to the coronavirus is reasonable.

By recording the time of possible exposure, of the onset of symptoms, onset of fever, and detection by authorities for each individual case, U.S. scientists created a model of incubation period distribution, which is nothing more than the time between the time an individual is exposed to the disease and the time he or she begins to show symptoms. This usually occurs before the contagious period, when transmission of the disease to other people is likely to occur.

Analysis suggests that approximately 97.5% of people who develop symptoms of SARS-CoV-2 infection will do so within 11.5 days of exposure. Researchers estimated that for every 10,000 individuals quarantined for 14 days, only 101 would develop symptoms after being released from quarantine.

For the study, experts analyzed 181 cases from China and other countries that were detected before Feb. 24, and were documented in the media and included likely dates of exposure and symptom onset. 

"Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although that period of time would lose some cases over the long term," said Justin Lessler, an associate professor in the Department of Epidemiology at the Bloomberg School and leader of the study published in the Annals of Internal Medicine.

The figures

The Johns Hopkins team found that less than 2.5 per cent of those infected showed symptoms within 2.2 days; the average estimated incubation period was 5.1 days, and 97.5 per cent showed symptoms within 11.5 days.

There has been concern that the incubation period was not long enough after other teams of researchers discovered incubation periods lasting up to 19 and 24 days.

"A study of patients who left the hospital in the province of Canton found that 14% of the cases were positive again. In Wuhan they have decreed 14 days of isolation for patients who are considered cured. Therefore, it is now suspected that the maximum incubation period of the coronavirus can be up to 24 days, and not 14," explains VERY Daniel Orts, a preventative doctor and outreach worker.

More research will be needed, with larger groups, to confirm whether a longer incubation period will cause a problem for our current quarantine policies. In any case, if you feel sick, stay home.


Reference: The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases Estimation and Application. Annals of Internal Medicine (2020).

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