Charting an Omicron Infection - The New York Times

In less than two months, the Omicron variant of the coronavirus has spread around the globe and caused a staggering number of new infections.

Omicron now accounts for more than 99.5 percent of new infections in the United States, according to estimates from the Centers for Disease Control and Prevention.

The time that elapses between when someone is first exposed to the virus and when they develop symptoms is known as the incubation period.

average incubation period.

incubation period.

Research suggests that the original version of the coronavirus and early variants had an incubation period of about five days, on average.

The Delta variant seems to move faster, with an average incubation period of about four days.

Omicron is swifter still, with an incubation period of roughly three days, according to a recent C.D.C.

In a recent study of the Alpha and Delta variants, researchers found that people tended to reach their peak viral loads about three days after infection and clear the virus about six days after that, on average.

In one preliminary study, researchers found that Omicron infections were about a day shorter than Delta infections and resulted in slightly lower peak viral loads, on average

But the difference might be due to higher rates of pre-existing immunity — as a result of vaccination or prior infection — among the people who were infected with Omicron

Another research team found that among vaccinated people with breakthrough infections, Omicron and Delta produced similar levels of infectious virus

One small study found that antibodies produced after an Omicron infection seem to protect against Delta, but Delta infections offer little protection against Omicron

If the finding holds up, it means that Delta may soon have trouble finding hospitable hosts — and that Omicron is likely to replace Delta rather than co-exist with it

Omicron appears to cause less severe disease than Delta

In one recent study, researchers found that people with Omicron infections were less likely to be hospitalized, end up in the I.C.U

or require mechanical ventilation than those with Delta infections

One possible explanation is that Omicron is less likely to damage the lungs than previous variants

One indication of reduced severity is that unvaccinated people seem less likely to be hospitalized with Omicron than with Delta

But Omicron’s apparent mildness may also stem from the fact that it is infecting far more vaccinated people than Delta did

Omicron is skilled at evading the antibodies produced after vaccination, which is leading to more breakthrough infections, but vaccinated people are still protected from the most severe disease

Still, doctors cautioned, although the variant may be milder on average, some patients, especially those who are unvaccinated or have compromised immune systems, may become severely ill from Omicron infections

Because Omicron replicates so fast and the incubation period is so short, there is a narrower window in which to catch infections before people begin to transmit the virus

Earlier in the pandemic, people were advised to use a rapid test five to seven days after a potential exposure to the virus

Given Omicron’s shorter incubation period, many experts now recommend taking a rapid test two to four days after a potential exposure

People who are testing to reduce the risk of transmitting the virus to others, for example at an upcoming gathering, should test as close as possible to the event itself, experts said

recently loosened its isolation guidelines for people who are infected with the virus

Previously, the agency recommended that people who test positive for the virus remain isolated for 10 days

The new guidelines say that infected people can leave isolation after five days if they are asymptomatic or their symptoms are resolving and they are fever-free

People should wear well-fitting masks for an additional five days when around other people

isolate for 5 days

isolate 10 days

isolate 5 days

The agency said these changes were prompted by data suggesting that transmission of the virus is most likely in the day or two before symptoms appear and the two or three days after

But scientists have noted that some people may be infectious for longer than that, and some criticized the agency for not recommending that people receive a negative result on a rapid test before ending their isolation periods

The agency subsequently updated its guidelines to note that people who wanted to test should take a rapid antigen test “towards the end” of the five-day isolation period but stopped short of formally recommending it