It takes five days on average for coronavirus symptoms to show, experts believe – although it could take much longer. A study found that the typical incubation period of Covid-19 was 5.1 days, suggesting the current self-isolation recommendation of 14 days is ‘reasonable’.
Almost all (97.5%) of people who developed symptoms appeared to do so within 11.5 days of infection, however a small minority took more than this to show symptoms. By contrast, the types of coronaviruses in humans that cause common colds have average incubation periods of around three days.
Experts, led by researchers from the Johns Hopkins Bloomberg School of Public Health in the US, studied 181 cases of people confirmed to be infected with the new coronavirus, which causes the respiratory illness Covid-19.
The researchers conducted an analysis of news reports, public health reports, and press releases which included information on likely dates of exposure and when symptoms started. Most of the cases were linked to Wuhan, the city in China at the center of the outbreak, and the surrounding Hubei province.
The authors conclude that current ‘self-isolation’ time frames adopted by health bodies iare ‘reasonable’.
Some people who have, or may have, been infected have been asked by health officials to stay away from others for two weeks – or ‘self-isolate’ – to reduce the risk of the infection spreading.
The authors of the analysis said however that a small number of cases could develop symptoms after this quarantine period is over. The estimates, published in the journal Annals of Internal Medicine, estimates that 101 out of every 10,000 cases will develop symptoms after 14 days of active monitoring or quarantine.
‘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.