Study: Omicron has shorter incubation than other COVID-19 strains

Aug. 22 (UPI) -- A new study suggests that with the evolution of mutant strains, the mean incubation period of COVID-19 decreased gradually from five days for cases caused by the Alpha variant to 3.42 days for the Omicron variant.

COVID's Beta and Delta variants were in the mid range, at 4.5 days and 4.41 days, respectively, the research found.

It's important to identify the incubation period of different COVID-19 variants to best determine how long people should isolate to avoid spreading the virus, said the researchers, who are based in China, said.

They said their research might help adjust prevention and control strategies and better block the transmission of COVID-19.

The research findings were published Monday in JAMA Network Open.

The researchers said their work suggests that "SARS-CoV-2 has evolved and mutated continuously throughout the COVID-19 pandemic, producing variants with different enhanced transmission and virulence."

They noted that COVID-19 transmission remains difficult to contain. By March, it had resulted in more than 460 million confirmed cases and 6 million deaths worldwide over the course of the ongoing pandemic.

The study, which included a review of 142 studies with 8,112 patients, also found differences in incubation periods due to age and severity of illness.

The mean COVID-19 incubation was 7.43 days among people over the age of 60, compared with 8.82 days among infected children 18 years old or younger.

It was 6.99 days among patients with mild to moderate illness versus 6.69 days among patients with severe illness.

The researchers noted that many studies have been conducted around the world to estimate the average incubation period of COVID-19.

"However, the reported estimates of incubation period in these fragmented studies vary depending on the number of study participants recruited, the type of design employed, the data collection period, and the country in which the study was conducted," they said.

Also, they said, the spread of the Delta and Omicron variants means that the current incubation period of COVID-19 is different from that in the initial outbreak of Wuhan.

According to the Centers for Disease Control and Prevention, COVID-19 symptoms may appear any time from two to 14 days after someone is exposed to the virus.