Omicron: What We Know About the New Covid Variant

In just a few weeks since its discovery, Omicron has turned out to be highly transmissible and less susceptible to vaccines than other variants.,


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What is the Omicron variant?

First identified in Botswana and South Africa in November, this new iteration of the coronavirus has prompted concern among scientists and public health officials because it carries an unusually high number of mutations that make it more transmissible and less susceptible to existing vaccines.

On Nov. 26, the World Health Organization designated Omicron a “variant of concern” and warned that the global risks posed by it were “very high,” despite what officials described as a multitude of uncertainties. Since then, the variant has been identified in nearly 60 countries, according to the W.H.O., on every continent except Antarctica. At the beginning of December, a California resident who returned home from South Africa was identified as the first American infected with Omicron. Officials have since detected the variant in 27 states.

What do we know about Omicron’s presence in the U.S.?

It’s too early to say how widespread the variant will become in the United States. But experts like Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, cautioned that the number is likely to markedly increase in the coming weeks.

On Dec. 10, the C.D.C. released a report on the first 43 cases identified in the United States. Only about one-third of those infected with Omicron had traveled internationally in the two weeks before testing positive or developing symptoms. That finding indicated that Omicron was already spreading within the United States from person to person.

The study also offered early hints of how well the variant can overcome vaccination and immunity from previous infections. The majority of people infected with Omicron — 34 individuals — were fully vaccinated when they developed symptoms or tested positive for Covid. Fourteen had received a booster dose as well, while six had previously been infected with the coronavirus.

Only one of the 43 people required hospitalization, and none died. That doesn’t necessary mean that Omicron is mild compared to other variants. For one thing, the sample was too small to be representative. What’s more, young adults under 40 accounted for most of the cases. Older people are at far higher risk of severe Covid.

Should we be worried?

The discovery of Omicron prompted swift responses from governments worldwide. A number of countries banned flights from southern Africa, or — like Israel, Japan and Morocco — barring entry of foreign travelers altogether.

Many public health experts criticized the move, arguing that Omicron had been around for weeks and had likely spread to many countries undetected. Once researchers began looking for Omicron around the world, that proved to be true.

On Dec. 9, President Biden further tightened restrictions for international travelers coming to the country.

In the first days after Omicron’s discovery, scientists could not say much about Omicron’s threat. They could see that it had mutations shown in other variants to speed up their transmission and allow them to partially evade immune responses. But they had to wait for more evidence to emerge to get a clearer picture of its nature.

Within a few weeks, early results of studies started coming to light. While some uncertainties remained, this evidence made it clear that Omicron poses a serious threat worldwide. “It rules out some of the rosier futures,” said William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.

Does Omicron spread faster than other variants?

Epidemiologists will need weeks to work out just how well Omicron spreads compared to other variants. There are many ways in which a mediocre variant may appear to be much better at getting from host to host. For example, a few random superspreader events can give the illusion that a variant is inherently more contagious.

The evidence so far does indicate that Omicron spreads faster than other variants — even Delta, which until now was the fastest spreading variant yet found. The earliest evidence came from South Africa, where Omicron rapidly grew to dominance in one province after another. In other countries, researchers have been able to catch Omicron earlier in its upswing, and the picture is the same: Omicron cases are doubling every two or three days — a much shorter time than Delta needed to double.

For a closer look at how well Omicron spreads, British researchers also observed what happened in the households of 121 people who got infected with the variant. They found that Omicron is 3.2 times more likely to cause a household infection than Delta.

Researchers do not yet know why Omicron spreads so readily. One possibility is that it can invade cells more readily; other possibilities include an ability to multiply once inside cells.

Does immunity from previous infections stop Omicron?

Not very well. One reason that the Omicron-driven surge in South Africa was so surprising is that the country had already experienced extensive waves of Covid caused by earlier variants. As the result, the majority of South Africans had been infected at some point in the pandemic. Despite that immunity, a large number of South Africans have become infected once more with Omicron.

British researchers found similar results in a study they published on Dec. 10. They found that many people with Omicron had already had survived Covid. The researchers estimated that the risk of reinfection with Omicron is about five times greater than that for other variants.

This ability to evade immune defenses is probably part of the explanation for why Omicron cases are doubling so quickly. While other variants are getting knocked out by antibodies, Omicron is succeeding in infecting more cells — making it more successful at getting into more people.

How much protection do vaccines provide?

When Omicron surfaced in South Africa, only 30 percent of the country’s had been vaccinated. That low vaccination rate made it difficult to determine how effective vaccines were against Omicron. Researchers at vaccine companies and academic labs quickly launched laboratory studies to get some clues.

They mixed antibodies from vaccinated people with Omicron viruses in Petri dishes of human cells. Then they waited to see how well the antibodies blocked the viruses from replicating.

The first batch of experiments came to the same basic conclusion: Antibodies from the Pfizer-BioNTech vaccine were much less successful at stopping Omicron than they were against earlier variants. But people who got a third booster shot produced much higher levels of antibodies, which do a better job fighting Omicron.

Early epidemiological studies arrived at similar conclusions. In Britain, researchers found that after six months, two doses of the AstraZeneca vaccine provided no protection at all from infection from Omicron. Two doses of Pfizer-BioNTech had an effectiveness of just 34 percent. But a Pfizer-BioNTech booster had an effectiveness of 75 percent against infection.

These results have reinvigorated vaccination efforts and spurred widespread booster campaigns in many countries to prepare for Omicron surges in the weeks to come.

Can vaccines reduce the severity of Covid?

Scientists strongly suspect this will be the case, but they need more direct evidence to know for sure.

In addition to producing antibodies to coronaviruses, the vaccines also stimulate the growth of T cells that help fight the disease. T cells learn to recognize when other cells are infected with coronaviruses and then destroy them, slowing the infection. The mutations that allow Omicron to evade antibodies are not expected to let it escape the recognition of T cells.

If this turns out to be the case, scientists expect that Omicron will be very good at causing infections in vaccinated people, but will be much less likely to advance to severe disease. The result would be more mild to moderate cases, with fewer hospitalizations. Boosters will likely be even more effective at preventing severe disease.

How bad will a Covid case caused by Omicron be?

The early Omicron cases raised hopes that the variant might cause milder disease than other variants. But it’s too soon to know if that’s true.

The Coronavirus Pandemic: Key Things to Know

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The Omicron variant. The latest Covid-19 variant, which has been detected in dozens of countries, seems to dull the power of the Pfizer vaccine, but the company said its boosters offer significant protection. Omicron appears to spread rapidly, though it may be less severe than other forms of the virus.

A new wave worries Britain. With cases of the Omicron variant doubling every three days and the government introducing new restrictions, the country is bracing for a new coronavirus surge.

Vaccine mandates in Europe. The latest wave of the pandemic is prompting countries like Germany and Italy to impose restrictions that single out those who are not vaccinated. The measures are rekindling the debate over governments’ right to curtail individual liberties in the name of public health.

Boosters. The F.D.A. authorized Pfizer to provide boosters to 16- and 17-year olds on an emergency basis, six months after receiving their second dose of the Covid vaccine. The C.D.C. promptly signed off on the move. Pfizer recently said that a booster shot of its vaccine offers significant protection against Omicron.

The worldwide vaccination campaign. One year into the global vaccine rollout, the gap in vaccination rates between high- and low-income countries is wider than ever. Challenges in Zambia highlight how infrastructure issues and the public’s hesitancy to get vaccinated are proving to be large obstacles.

In South Africa, where Omicron created its first known surge, doctors reported seeing fewer severe cases than in earlier waves of Covid. In fact, they often only became aware that their patients were infected with the coronavirus after they were admitted for other conditions.

But a large fraction of the patients South African doctors were seeing were younger. They were therefore much less likely to have severe Covid than older people. Likewise, in Europe the earliest cases of Omicron involved people who had traveled from southern Africa. These travelers tended to be younger and healthy, reducing their risk of severe disease.

Before we can know whether Omicron is milder than other variants, epidemiologists will have to wait for more people to get infected with Omicron, and then wait several more weeks to see how many of them progress to severe disease.

Is Covid caused by Omicron still treatable?

Yes. Omicron can evade some monoclonal antibodies, but GSK has reported that its formulation, called sotrovimab, will probably remain effective. Medications that rein in dangerous inflammation, such as dexamethasone, will also work.


Staff members standing before an arrivals information board at Haneda International Airport in Tokyo. A number of countries banned flights from southern Africa or, in the case of Israel, Japan and Morocco, barring entry of foreign travelers altogether.Credit…Franck Robichon/EPA, via Shutterstock

Merck, Pfizer and other companies are developing antiviral pills against Covid, and while they have yet to test the pills against Omicron, there’s good reason to expect them to work. Many of Omicron’s mutations are in the gene for a surface protein called spike, which is the target of antibodies. But antiviral pills like molnupiravir target other proteins that are mostly unchanged in Omicron.

What will Omicron do over the next few months?

Researchers are creating mathematical models to figure out what Omicron will do in the months to come. These models, by necessity, are based on assumptions about the variant, and those assumptions may need to be altered as more evidence comes to light. But scientists can already see that Omicron is very transmissible and adept at evading immune defenses.

Researchers now expect Omicron to become dominant in many countries by the end of the year. It may then go on to create a huge wave of cases in the weeks that follow. Even if Omicron does turn out to be milder, it could still push hospitals to their limit. A smaller fraction of Omicron cases may require hospitalization, but if the number of Omicron cases is much bigger than in previous surges, there will still be more seriously ill patients to treat.

But disease projections are not carved in stone. The variables can change if more people get vaccinated and practice safety measures in public like social distancing and mask-wearing that help contain the spread. Boosters will create an even stronger wall of defense.

Some governments are already taking further actions to fight Omicron. Denmark, for example, sent students home on Dec. 10, closed bars and took other measures to reduce crowds. And Britain has reimposed several measures, and encouraged citizens to work from home.

Why is it called Omicron?

When the W.H.O. began to name emerging variants of the coronavirus, they turned to the Greek alphabet — Alpha, Beta, Gamma, Delta and so on — to make them easier to describe. The first “variant of concern,” Alpha, was identified in Britain in late 2020, soon followed by Beta in South Africa.

But veterans of American sorority and fraternity life might have noticed the system has skipped the next two letters in the alphabetical order: Nu and Xi.

Officials thought Nu would be too easily confused with “new,” but the next letter, Xi, is a bit more complicated. W.H.O. officials said it was a common last name, and therefore potentially confusing. Some noted that it is also the name of China’s top leader, Xi Jinping.

A spokesman for the W.H.O. said the organization’s policy was designed to avoid “causing offense to any cultural, social, national, regional, professional, or ethnic groups.”

Next in line? Omicron. (Here’s how it’s pronounced, and here.)

Emily Anthes contributed to this article.

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