What Is Omicron’s Incubation Period?

The incubation period of a virus is the number of days between the time a person gets infected and when symptoms begin to appear. For COVID-19, this can reach up to 14 days after virus exposure.

The average incubation period tends to differ among COVID-19 variants, and data suggest that it may be shorter for Omicron. Here’s what that means for infected individuals.

How Does Omicron Compare to Previous Variants?

Each new variant may have its own variations in incubation periods.

“With the original COVID-19 variant, symptoms showed up on average around five to six days after contact with an infected person, [while] the Delta variant’s incubation period was around four days,” Beth Oller, MD, a family physician at Solomon Valley Family Medicine, told Verywell. “Some data suggest the incubation period for Omicron may be closer to three days.”

Data from December 2021 suggests that Omicron’s average incubation period is around two to four days, which would mean that symptoms may develop faster after exposure compared to other variants. At this time, the BA.1 subvariant was the dominant strain.

As the virus evolves, new subvariants emerge and become the dominant variant. One study looked at data from July-August 2022 found the average incubation time of the BA.5 variant to be 2.6 days.

Omicron’s average incubation period doesn’t mean that people who don’t get symptoms four days after exposure are not infected.

The mean and median incubation periods are usually the ‘quick’ answers, but it’s also important to know the shape of the curve to understand how many outliers there are and for how long the period is, Stanley H. Weiss, MD, professor of medicine at the Rutgers New Jersey Medical School and professor of biostatistics and epidemiology at the Rutgers School of Public Health, told Verywell.

It’s still important for everyone to get tested regularly if they’ve been exposed to ensure that they are not inadvertently spreading the virus, especially since people are infectious before symptoms appear.

When Are You Most Contagious?

It appears that a person is likely to be most infectious one to two days before symptoms appear, which continues for a few days after the symptoms begin, Weiss said.

In May 2023, the CDC updated their guidance and has since recommended reducing the isolation period of infected individuals to five days if their symptoms have fully resolved. The CDC says the majority of virus transmission occurs one to two days before symptom onset and two to three days after.

“The decrease in isolation time was largely to decrease the impact and disruption of infection on day-to-day life and allow people to return to work sooner,” Oller said. “These recommendations, however, are only for asymptomatic and mildly ill people, and the shortening to five days means that a person should be isolated during the period when a person is most infectious.”

A study published in Clinical Microbiology and Infection found that individuals with COVID-19 remain contagious after the fifth day of illness—regardless of symptom status—which means including individuals on their days six to 10 of illness in work settings may increase the spread of the virus.

Therefore, isolating for five days may not be enough, even if one is asymptomatic, Weiss said. The rapid antigen test may help gauge infectiousness: If a person tests positive, they should consider themselves contagious, he added.

Moreover, it is still necessary to wear a well-fitting mask and stay away from other people as much as possible for about five days after leaving isolation, experts said. At the moment, there aren’t enough data to say for sure whether vaccination shortens the incubation period.

“There are arguments that could be made both towards shortening or lengthening,” Weiss said. “In part, I think [the incubation period] strongly depends upon the infected human.”

A 2021 study published in BMC Public Health found that the incubation period of the virus may vary by age. Overall, it’s important to get vaccinated against COVID-19 to have protection against severe outcomes of the virus. 

“The best way to protect yourself and those around you is to get vaccinated,” Oller said. “While long COVID, hospitalization, or death is less likely if a person is vaccinated, it is still possible and is not a risk that most of us want to take. Get vaccinated, encourage those you love to get vaccinated and get boosted when it is recommended.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.