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What we know — and don’t know — about the omicron variant

Early studies are beginning to paint a picture of omicron symptoms, vaccine effectiveness and the Covid variant's spread around the world.
A 3D rendering of Covid-19 variant B.1.1.529, dubbed omicron.
A 3D rendering of the Covid-19 variant B.1.1.529, dubbed omicron.CIPhotos via Getty Images

As omicron cases multiply around the world, scientists are racing to characterize the heavily mutated coronavirus variant to understand how it spreads, and gauge new risks during this wave of the pandemic.

Preliminary studies released this month have offered some clues about the effectiveness of vaccines against the latest variant and whether it causes more severe illness, but much remains uncertain and more research is needed. 

Here’s what is known so far about the omicron variant.

Why is omicron a concern?

Variants like omicron are the biggest threat to any end to the pandemic — and scientists warn that they will continue to emerge as the virus spreads.

The omicron variant features more than 30 mutations to the virus’s spike proteins, which cover the outside of the virus and are the main targets of vaccines and treatments like monoclonal antibodies. 

It’s possible that the mutations help the variant spread more easily and that they could enable it to evade protective antibodies generated by vaccines or through natural immunity from previous infections. The World Health Organization said in an update Dec. 14 that the omicron variant is spreading faster than any previously detected strain of the coronavirus.

Does it cause more severe illness or symptoms?

Evidence so far doesn’t suggest that’s the case, but it may be too early to tell.

Early reports suggest that for most people, at least for those who are up to date on their Covid vaccines, omicron appears to result in mild illness that can resemble the common cold. Cough, fatigue or tiredness and congestion and runny nose also appear to be prominent symptoms from omicron. It's less clear, however, whether the types of symptoms and their severity differ for those who are unvaccinated.

More research is needed, but early evidence suggests that the incubation period, or the time it takes for an infected person to develop symptoms after an exposure, may be shorter for omicron than for previous variants.

Preliminary research from Public Health Scotland found that people who were infected with the omicron variant in November and December were about two-thirds less likely to be hospitalized, compared with the delta variant.

Another study, from South Africa’s National Institute for Communicable Diseases, had similar findings, suggesting that people with the omicron variant were more than three-quarters less likely to be hospitalized.

The first major real-world analysis of the variant, released this month, looked at cases in South Africa, where it was first identified last month. The results suggest that it may cause less severe illness than the delta variant, which is still the dominant strain of the coronavirus in most countries. South African health officials found that on average, 29 percent fewer people were being admitted to the hospital than during the previous wave of delta infections. 

In a Dec. 17 update, South Africa's health minister said hospitalizations in the country have been significantly lower than during previous waves of infection. In the second week of South Africa's omicron wave, less than 2 percent of Covid-19 cases resulted in hospitalization, compared to 19 percent in the second week of the country's delta wave, Bloomberg reported.

There are also early indications that cases may be peaking already in Gauteng, South Africa's most populous province and the epicenter of the country's current outbreak.

Although the data are encouraging, experts have said it’s too soon to know whether the omicron variant does, indeed, cause milder illness or whether other factors, including South Africa’s younger population, play a role.

In the United States, the first few dozen confirmed omicron cases have been mostly mild, the Centers for Disease Control and Prevention said. 

The CDC studied 43 people infected with the variant, one of whom was hospitalized for two days, and found that the most commonly reported symptoms were cough, fatigue and congestion or a runny nose. More than three-quarters of the participants were fully vaccinated, and one-third of those people had also had the booster shot, according to the CDC.

CDC Director Dr. Rochelle Walensky called the report a “starting point,” adding that the agency will continue to closely monitor the variant. Experts have also cautioned that even if the omicron variant does cause less severe illness, big spikes in infections could still overwhelm health care systems in hard-hit countries.

Is it more contagious?

Most early research suggests that the omicron variant is more contagious than earlier strains of the coronavirus, but a definitive picture of its transmissibility isn’t yet known. 

Case numbers in hard-hit places, such as South Africa and the United Kingdom, are increasing exponentially, which suggests that the variant is highly transmissible, but research continues. After Omicron was first identified in South Africa last month, it took less than three weeks to become the dominant variant in the country. It has also overtaken the delta variant and become dominant in England and Scotland, according to health officials in the United Kingdom.

Omicron is also thought to be the dominant coronavirus variant now in the U.S., according to the CDC. As of Friday, more than 73 percent of new cases in the country were caused by omicron, according to data posted Monday by the agency.

Are vaccines effective against omicron?

Experts have expressed concerns that the variant’s mutations could allow it to dodge some protective antibodies generated by Covid vaccines. 

Early laboratory studies indicate that it may be somewhat resistant to vaccines, although it probably doesn’t evade them entirely. More research is needed, however, to understand what the preliminary findings mean in real-world settings.

An analysis released Dec. 14 by South Africa’s largest health care administrator found that two shots of the Pfizer-BioNTech vaccine were 70 percent effective at protecting against hospitalization from infection with the omicron variant, compared to 90 percent protection against hospitalization from the delta variant.

Preliminary data also found that the booster shot could play a key role in countering the drop in antibodies against omicron.

Moderna announced Monday that its half-dose booster shot significantly raised antibody levels that appear to provide protection against omicron in laboratory tests. The currently authorized booster demonstrated a 37-fold increase in antibody levels compared to levels before the booster, the company said. A full 100-microgram booster dose, meanwhile, caused a roughly 83-fold increase in neutralizing antibody levels.

The results have not yet been published or independently reviewed, and it remains to be seen how the booster performs in clinical settings.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and President Joe Biden's chief medical adviser, said Dec. 15 that booster shots likely won't need to be reformulated to target omicron.

"Our booster vaccine regimens work against omicron," he said. "At this point, there is no need for a variant-specific booster."

Moderna announced, however, that it is developing an omicron-specific booster that could advance into clinical trials in early 2022.

Pfizer announced earlier this month that a booster dose strongly protects against the new variant in laboratory tests — similar to levels of protection that the company’s initial two-dose regimen offered against the original strain — although the findings must be confirmed in real-world settings.

A preprint study that has yet to be peer reviewed found that China's Sinopharm vaccine, Russia's Sputnik vaccine and the vaccine developed by Johnson & Johnson generate low levels of protective antibodies against omicron. The research, led by scientists at the University of Washington and a Swiss biotech company called Humabs BioMed SA, offers preliminary results on how various vaccines available around the world may hold up against the heavily mutated variant.

The early studies have been in line with initial suspicions from vaccine makers that the variant could sidestep some protection from vaccines, but scientists have also emphasized that the immune system has other tools that could likely enable it to recognize and fight the virus, even if antibody levels wane. 

While the variant may increase the chances of breakthrough infections in those who have been vaccinated, there are no indications so far that vaccinated people infected with it experience more severe symptoms compared to other variants.

Where is it spreading?

Cases have been confirmed in at least 89 countries, according to the World Health Organization. 

“The reality is that omicron is probably in most countries, even if it hasn’t been detected yet,” WHO Director-General Tedros Adhanom Ghebreyesus said earlier this month.

The first case in the U.S. was confirmed Dec. 1 in California. Omicron infections have since been detected in all 50 states and Washington, D.C., and the variant now accounts for nearly three-quarters of new cases in the country, according to the CDC.

There are signs that the omicron variant is spreading faster than the delta variant and will soon overtake delta in the U.S., according to Andy Slavitt, a former senior adviser to the White House Covid response team. Omicron infections appear to be doubling every two to four days in the country, he said. At that pace, omicron cases could peak in the U.S. in the third week of January.

Are kids at risk?

It’s not yet known whether the variant poses a higher risk to infants and children compared to previous variants. 

Scientists are closely monitoring regions of the world where the omicron variant is spreading widely, including South Africa and the U.K., to better understand its effect on children.