The time between exposure to SARS-CoV-2 virus and the onset of symptoms — or incubation period — has shortened with the advent of each new viral variant, a new study finds.
Investigators in China performed an analysis of 142 studies including over 8,000 patients. The alpha variant, which emerged in the city of Wuhan in 2019, had an average incubation period of 5 days. The incubation time shortened to 4.5 and then 4.4 days when the beta and delta variants emerged as a key source of infections in 2020 and 2021. It has since fallen to 3.4 days with the advent of the currently dominant omicron variant, they reported.
At the same time, the virus has become more transmissible, although apparently less deadly overall.
Determining the incubation period of dominant variants helps to determine the most effective patient isolation periods, and to make contact tracing and testing decisions aimed at preventing the spread of the disease. Although incubation time varies per person no matter the variant, average incubation periods can help in setting public policy, the researchers said.
“At present, based on the assumption that the incubation period of COVID-19 is 1 to 14 days, the [World Health Organization] still recommends that COVID-19 close contacts be isolated for 14 days,” said Wannian Liang, PhD, of Tsinghua University, Beijing, in a statement.
COVID-19 seems to have a longer incubation period than do other acute respiratory viral infections, such as the common cold, at 3.2 days, for example, Liang and colleagues reported.
Notably, the current study found that the average incubation period was shorter (at 6.7 days) in COVID-19 patients with severe illness than in patients without severe illness, the researchers added.
Full findings were published in JAMA Network Open.
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