SARS-CoV-2 has evolved an incubation time more like seasonal coronaviruses
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The incubation period for COVID-19-the time between when SARS-CoV-2 first infects a person and when resulting COVID-19 symptoms first appear-has gradually shortened as the pandemic has stretched on and the virus has mutated. That's according to a new meta-analysis published this week in JAMA Network Open by researchers in Beijing, who harvested data on over 8,000 patients from 142 COVID-19 studies.
When the original version of the novel virus mushroomed out of Wuhan, China, the mean incubation period was 6.65 days, according to pooled data from 119 studies. But then, the incubation period got shorter as the variants evolved. The alpha variant had a mean incubation of 5 days, according to one study; beta, 4.5 days, according to another; delta had a mean of 4.41 days, according to pooled data from six studies; and now with omicron, the incubation period has shrunk to 3.42 days, according to data from five studies.
The current shortened incubation period now puts SARS-CoV-2 more in line with commonplace respiratory viruses, including the four human coronaviruses that circulate seasonally and cause mild infections similar to the common cold. Their incubation period is 3.2 days. Rhinovirus, the most common cause of the common cold, has a mean incubation period of 1.4 days. For influenza, it can range from 1.43 to 1.64 days, and parainfluenza has a mean of 2.6 days.