Omicron: What We Know About the 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.,

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

What is the Omicron variant?

First identified in Botswana and South Africa in November, the Omicron variant has surged around the world over the past few weeks, faster than any previously known form of the coronavirus. While there’s a lot that scientists have yet to understand about Omicron, what they know already makes it clear that the variant could cause a huge number of new cases in the weeks to follow and that it could push some hospital systems to the breaking point.

Scientists first recognized Omicron thanks to its distinctive combination of more than 50 mutations. Some of them were carried by earlier variants such as Alpha and Beta, and previous experiments had demonstrated that they could enable a coronavirus to spread quickly. Other mutations were known to help coronaviruses evade antibodies produced by vaccines.

Based on those mutations, along with a worrying rise in Omicron cases in South Africa, the World Health Organization designated Omicron a “variant of concern” on Nov. 26, warning that the global risks posed by it were “very high.” Since then, the variant has been identified in more than 80 countries. 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 more than three dozen states. Omicron is quickly surging to dominance in many parts of the world, living up to the potential that scientists recognized when it was first discovered.

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

Scientists estimate that cases in the United States are doubling about every two to four days. That pace puts it on track to become the dominant variant in the country in the next few 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. Researchers will get a clearer picture of Omicron’s impact on the United States in the weeks to come.

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 — barred entry of foreign travelers altogether. On Dec. 9, President Biden further tightened restrictions for international travelers coming to the country.

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

The rapid doubling rate of Omicron means that it may soon become the dominant variant in many countries. It could then go on to a record-breaking number of infections, even among vaccinated people or those who had previously had Covid-19. But it’s not clear yet just how big a risk Omicron poses to any given person who gets it.

Does Omicron spread faster than other variants?

Yes. It is two to three times as likely to spread as Delta.

The earliest evidence for Omicron’s swift spread 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 to four 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 had been infected with the variant. They found that Omicron was 3.2 times as likely to cause a household infection as Delta was.

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. The first clues that Omicron could evade immunity came from South Africa, where scientists estimate that at least 70 percent of people have had Covid-19 at some point in the pandemic. An unexpectedly large fraction of Omicron cases involved people who had previously been infected.

When Omicron surged in England, British researchers similarly found that many people infected with the new variant had already survived Covid. The researchers estimated that the risk of reinfection with Omicron was about five times that of other variants.

For a deeper understanding of this increased risk of reinfection, a number of teams of scientists have studied the antibodies produced by people who recover from Covid-19. If they mix those antibodies in a dish with other variants, the antibodies do a good job of preventing the viruses from infecting human cells.

But if they mix those antibodies with Omicron, it still manages to get inside the cells much of the time. That means that the mutations Omicron carries are changing the shape of its surface proteins, where antibodies lock onto the coronavirus.

This ability to evade immune defenses is probably part of the explanation as to 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 do vaccines protect against an Omicron infection?

Several studies indicate that full vaccination plus a booster shot provides strong protection against infection with Omicron. Without a booster, however, two doses of a vaccine like Pfizer-BioNTech’s or Moderna’s provide much less protection. (Still, two doses of a vaccine do appear to protect against severe disease from Omicron.)

Scientists drew blood from fully vaccinated people and mixed their antibodies with Omicron in a petri dish loaded with human cells. Every vaccine tested so far has done a worse job at neutralizing Omicron than other variants. And antibodies from people who received the AstraZeneca or Johnson & Johnson vaccines don’t seem to do anything at all against Omicron.

But when researchers tested antibodies from people who had received boosters, they saw a different picture. Boosted antibodies blocked many Omicron viruses from infecting cells.

Researchers found a similar response when they looked at people who had been fully vaccinated with two doses after a Covid-19 infection: Their antibodies were extremely potent against Omicron.

Real-world studies support the results of these experiments. In South Africa, researchers found that two doses of the Pfizer-BioNTech vaccine had effectiveness against Omicron infection of just 33 percent. Against other variants, its effectiveness is 80 percent.

In Britain, researchers found that people who had received two doses of the AstraZeneca vaccine enjoyed no protection at all from infection from Omicron six months after vaccination. Two doses of Pfizer-BioNTech had effectiveness of just 34 percent. But a Pfizer-BioNTech booster had effectiveness of 75 percent against infection.

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

Can vaccines reduce the severity of Covid?

Preliminary studies suggest that they can. In South Africa, researchers who reviewed the first three weeks of Omicron cases in the country’s largest health care system found that two doses of the Pfizer-BioNTech vaccine had effectiveness of 70 percent against hospitalization.

That finding fits well with what scientists know about how all vaccines work. In addition to producing antibodies, vaccines also stimulate the growth of T cells that help fight a particular disease. T cells learn to recognize when other cells are infected with specific viruses and then destroy them, slowing the infection.

Scientists are starting to examine the T cells produced by Covid-19 vaccines to see how well they fare against Omicron. Preliminary studies suggest that these T cells still recognize the Omicron variant.

This preliminary evidence suggests that Omicron is good at establishing itself in the noses of hosts, thanks to its ability to evade antibodies. But Omicron infections may not be able to get past the T-cell line of defense. By killing infected cells, T cells may make it harder for the virus to reach deep into the airway, where it can cause serious disease.

The Coronavirus Pandemic: Key Things to Know

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A new U.S. surge. The C.D.C said that the Omicron variant’s rapid spread in the U.S. may portend a surge in infections as soon as January, but cases are already spiking, leading offices to cancel holiday parties, Broadway performances to be shuttered and college finals to be moved online.

The Omicron variant. The new Covid variant has been detected in dozens of countries. While Omicron appears to be able to partially evade antibodies, it could be less severe than other forms of the virus, and new laboratory studies indicate that vaccines, and especially boosters, may offer protection against severe disease.

Biden’s vaccine mandate. A federal appeals panel on Dec. 17 reinstated a Biden administration rule requiring larger companies to mandate that their workers get vaccinated against Covid-19 or submit to weekly testing by Jan. 4. A day later, the Labor Department said that it would delay that deadline until Feb. 9.

Pfizer vaccine in younger children. The company said that a low dose of its coronavirus vaccine did not produce an adequate immune response in 2- to 5-year-olds in ongoing clinical trials. The setback threatens to keep the vaccine from younger children for longer than many had hoped.

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.

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 did not become aware that their patients had been infected with the coronavirus until after the patients were admitted with other conditions.

A study released on Dec. 14 from South Africa’s largest health care system found that hospital admissions were lower in the first three weeks of the Omicron surge than during previous waves driven by earlier variants — 38 per 1,000 admissions, compared with 101 per 1,000 during the Delta-driven wave and 131 per 1,000 when the Beta variant was dominant.

But that study may not necessarily be cause for comfort in other parts of the world. The average age of patients in the South Africa study was 34; older people are at greater risk of severe Covid-19.

As Omicron spreads more widely, the true impact of the variant will become clearer. But it’s important to understand that the severity of a variant depends not just on its own biology, but on the biology of its host.

It may very well turn out that a substantial fraction of people who get sick with Omicron will have mild cases because they are protected by their immune systems, thanks either to a vaccine or a previous infection. Even if a large percentage of people have only mild Covid-19 after contracting Omicron, the sheer number of cases may mean that hospitals get flooded with severe cases.

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.


Haneda International Airport in Tokyo. Japan is one of several countries that have barred entry of foreign travelers in light of the emergence of Omicron.Credit…Franck Robichon/EPA, via Shutterstock

Merck, Pfizer and other companies are developing antiviral pills against Covid. While Omicron has many mutations that can let it evade monoclonal antibodies, it has fewer mutations in the proteins targeted by the pills. Pfizer has reported that Paxlovid can bind to its target protein in Omicron just as well as it does in other variants. Belgian researchers have reported that the drug works against the variant in cell cultures.

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 is adept at evading immune defenses.

Researchers now expect Omicron to become dominant in many countries by the end of the month. The European Center for Disease Prevention and Control released a study on Dec. 15 projecting that Omicron would become dominant in the entire continent by January.

Even if Omicron does turn out to be milder than other variants, it could still push hospitals to their limits. 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. And in the United States, those Omicron cases will stack on top of already high levels of hospitalization driven by the Delta variant.

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 has 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 that 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 had been 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 reporting.

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