Covid-19 may take as much as 8 days to show symptoms: Scientists

The incubation period of Covid-19, which is the time after which those infected with the novel coronavirus start showing the first symptoms, could be as much as eight days -- longer than previous estimates of four to five days -- says a new study which involved the largest amount of patient samples to date in such an analysis.

The research, published in the journal Science Advances, identified pre-symptomatic individuals at their time of departure from the Chinese city of Wuhan, where the Covid-19 pandemic originated, and then followed these infected people until their symptoms developed.

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According to the scientists, including Chong You from Peking University in China, the existing estimates of four to five days for the incubation period were based on small samples sizes, limited data, and self-reports that could be biased by the memory or judgement of the patient or interviewer.

In the current study, they developed a low-cost approach to estimate incubation periods, and applied it to 1,084 confirmed cases of Covid-19 that had known histories of travel or residency in Wuhan.

The method has better accuracy by relying on a public database of dates of infection, and uses statistical methods to reduce recall bias -- the inaccurate recollection of past events, the scientists said.

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Using the new approach, the researchers calculated that the average incubation period was 7.75 days, with 10 percent of the patients showing an incubation period of 14.28 days.

They said the findings may concern health authorities relying on the standard 14-day quarantine, but cautioned that their approach relies on several assumptions and may not apply to later cases in different parts of the world where the virus may have mutated.