Sat. May 21st, 2022

In less than two months, the Omicron variant of coronavirus has spread across the globe, causing 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 nation reported as many as 800,000 new cases a day in mid-January, more than three times as many as at any earlier point in the pandemic.

Researchers have worked overtime to study Omicron. Many questions remain unanswered, but here is what they have learned so far.

Infection and incubation

Omicron is moving fast. It spreads rapidly through populations, and infections develop rapidly in individuals.

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

average incubation time


incubation period

Research suggests that the original version of coronavirus and early variants had an incubation period of about five days on average. The Delta variant appears to move faster, with an average incubation time of about four days. Omicron is still faster, with an incubation period of about three days, according to a recent CDC study.

Viral load

The amount of virus that builds up in a person’s body is known as viral load. Generally, people are thought to be most contagious when their viral load is high.

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

Whether Omicron follows the same pattern remains to be seen. In a preliminary study, the researchers found that Omicron infections were about a day shorter than Delta infections and resulted in a slightly lower maximum viral load on average. However, the difference may be due to higher rates of pre-existing immunity – due to vaccination or previous 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.

Other data suggest that Omicron may not work as earlier variants. Animal and laboratory studies indicate that it may not be as good at infecting the lungs as Delta, but that it may replicate more rapidly in the upper respiratory tract.

The variant can also have other unique properties. A small study showed that antibodies produced after an Omicron infection appear to protect against Delta, but Delta infections provide little protection against Omicron. If the finding holds, it means that Delta may soon have trouble finding hospitable hosts – and that Omicron is likely to replace Delta instead of coexisting with it.


Omicron appears to cause less serious illness than Delta. In a recent study, researchers found that people with Omicron infections were less likely to be hospitalized, end up in the intensive care unit, 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. A variant that primarily reproduces in the upper respiratory tract can cause less serious illness in most people. An indication of reduced severity is that unvaccinated individuals appear less likely to be admitted with Omicron than with Delta.

But Omicron’s apparent mildness may also stem from the fact that it infects far more vaccinated people than Delta did. Omicron is skilled at avoiding the antibodies produced after vaccination, leading to several breakthrough infections, but vaccinated people are still protected against the most serious disease. Booster shots of mRNA vaccines are 90 percent effective against hospitalization with Omicron, according to the CDC

Nevertheless, doctors warned that although the variant may be milder on average, some patients, especially those who are unvaccinated or have a weakened immune system, can become seriously ill from Omicron infections. And it’s too early to know if breakthrough cases of Omicron could result in prolonged Covid.


Because Omicron replicates so quickly and the incubation period is so short, there is a narrower window to catch infections before people start transmitting 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 time, many experts now recommend taking a rapid test two to four days after a potential exposure. (They also recommend taking at least two quick tests at approximately one-day intervals to increase the chances of detecting an infection.)

People who test 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.

There is still debate as to whether rapid antigen testing may be less sensitive to Omicron than other variants. PCR tests are more sensitive than rapid tests, which means they are likely to detect the virus earlier in the course of the infection, but it takes longer to return results.

New insulation rules

The CDC recently released its isolation guidelines for people infected with the virus. Earlier, the agency recommended that individuals who tested 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 disappear and they are fever-free. People should wear well-fitting masks for another five days when they are around other people.

avoid traveling,

wear a mask

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

However, scientists have noted that some people can be contagious for longer than that, and some criticized the agency for not recommending that people get a negative result on a quick 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 recommending it formally.

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