With each new COVID-19 variant, the interval between exposure and symptom development appeared to shorten, according to a study published Aug. 22 in JAMA Network Open.
COVID-19 is known to have a longer incubation period than other respiratory viral infections such as the flu, helping to explain why health agencies initially recommended a 14-day quarantine after exposure. Researchers from Peking University and Tsinghua University in Beijing analyzed data from 142 studies involving 8,112 patients to estimate whether the incubation period changed with different variants of the SARS-CoV-2 virus.
They found the mean incubation period pooled from all of the studies analyzed was 6.57 days.
That fell to an average of five days for the alpha variant; 4.5 days for beta, 4.4 days for delta and 3.4 days for omicron, the findings showed.
"Incubation period is one of the most important epidemiological parameters of infectious diseases," researchers said. "Identifying the incubation period of different variants is a key factor in determining the isolation period."
The CDC currently recommends people exposed to COVID-19 quarantine for five days followed by mask use for an additional five days.