Washington (AFP)
The incubation period for the new coronavirus that appeared in Wuhan, China is around 5.2 days on average, but varies widely among patients, according to Chinese researchers in one of the largest published studies to date on the epidemic of viral pneumonia.
The fact that the estimate is preliminary and "imprecise", and reveals large variations, justifies "a period of observation or quarantine of 14 days for those exposed", write the researchers of the Chinese health authorities in this study published in the major medical journal New England Journal of Medicine (NEJM).
The World Health Organization mentioned in a bulletin Monday a range of 2 to 10 days for the onset of symptoms (fever, cough, shortness of breath, even acute respiratory distress).
The Chinese estimate of the 2019-nCoV incubation periods was based on 10 patients. But the researchers studied the first 425 patients in total in order to establish two basic characteristics of the epidemic.
Early in Wuhan in December, the number of cases doubled every 7.4 days, according to their data.
They also estimate that each patient infected an average of 2.2 people, a figure called basic reproduction rate, or "zero R". This figure is not in itself predictive of the scale of an epidemic, but it is a useful parameter. In this case, it is relatively low, closer to winter flu (around 1.3) than measles, very contagious (more than 12), and comparable to the SARS of 2002 (3).
The researchers finally conclude that transmissions between humans "have occurred between close contacts since the middle of December 2019".
Two other analyzes released on Tuesday found average incubation periods of just a few days: 5.8 days, according to 34 patients studied by researchers in the Netherlands, with large differences; and three days at most in the case of a 27-year-old Vietnamese man infected by his father who returned from Wuhan, according to a letter published in the NEJM.
In the large Chinese study, half of the 425 patients were 60 or older. None were under the age of 15.
© 2020 AFP