This is *deep sigh of relief* news if you already got your booster or are planning to get one.
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Public health officials around the world have been closely watching the Omicron COVID-19 variant ever since the World Health Organization named it a "variant of concern" in late November. A huge question among doctors and the general public has been how well the COVID-19 vaccine will be able to protect people against Omicron.

Now, there are some answers. On Wednesday morning, Pfizer announced the results of an initial laboratory study on their vaccine and the Omicron variant. The study found that when someone has had three doses of the Pfizer-BioNTech vaccine (i.e. including the booster) their "neutralizing" antibody levels were 25 times higher against the Omicron variant than those in people with just two doses. Specifically, Pfizer said its vaccine and booster neutralized the Omicron variant to levels comparable to the efficacy of the original two-dose vaccine against earlier variants. (Which, FYI, all U.S. adults are now eligible to receive.)

If you haven't had a booster dose yet, Pfizer officials say you still have some protection against Omicron — but it's not as good as if you were boosted. In fact, Pfizer said that people without a booster had, on average, more than a 25-fold reduction in neutralizing antibodies (antibodies that defend a cell from a pathogen or infectious particle by neutralizing any effect it has) against the Omicron variant compared to other COVID-19 variants.

The company stressed this, though: The "vast majority" of vaccine-induced T-cells (which, like antibodies, help protect the body from infection) were not impacted by mutations in Omicron. As a result, Pfizer said they "believe that vaccinated individuals may still be protected against severe forms of the disease." However, they added, they're still "closely monitoring real-world effectiveness" of the vaccine against Omicron.

"Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it's clear from these preliminary data that protection is improved with a third dose of our vaccine," said Albert Bourla, chairman and chief executive officer of Pfizer, in a press release. "Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of COVID-19."

What does this mean for the COVID-19 vaccines and Omicron going forward? Here's what you need to know.

What Is the Omicron Variant, Again?

Omicron, aka B.1.1.529, is a variant of COVID-19 that was first detected in South Africa on November 9 and reported to the WHO on November 24. The WHO shared on November 26 that it had named Omicron a "variant of concern," the organization's most serious category for COVID-19 strains. The WHO said in a statement that infections in South Africa "have increased steeply" and happened to coincide with the detection of Omicron.

Since late November, Omicron has been detected in several more countries, including 18 states in the U.S., per data from the Centers for Disease Control and Prevention.

Early data suggests that Omicron is more infectious than previous strains, according to the WHO. It also has several mutations in its spike protein, which is the part of the virus that's used to latch onto your cells, says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York.

Because of the large number of mutations with Omicron, there have been concerns that this variant may be able to evade or partially evade the COVID-19 vaccine, says Dr. Russo. "Omicron is a highly divergent variant with a high number of mutations… some of which are concerning and may be associated with immune escape potential and higher transmissibility," according to the WHO.

What Does This Mean for the Other COVID-19 Vaccines?

It's not clear at the moment. Moderna CEO Stéphane Bancel told the Financial Times in a November 29 interview that the existing COVID-19 vaccines would not perform as well against Omicron. "There is no world, I think, where [the effectiveness] is the same level ... we had with Delta," he said. (The Delta variant is still the dominant strain in the U.S., causing 99.9 percent of COVID-19 cases, according to CDC data.)

While Moderna has not released data on how its vaccine performs against Omicron, it shared in late November that the company has a "comprehensive strategy" to help deal with new variants of concern, including a higher-dose booster shot. Johnson & Johnson said in a statement that it will evaluate its vaccine against Omicron, but the rest is TBD.

What This Might Mean for You

Dr. Russo says it's "not surprising" that the original Pfizer-BioNTech vaccine series is slightly less protective against Omicron. "We've already guessed that Omicron may be resistant to our vaccines," he says. "But we're getting a huge increase in antibodies with booster shots. The more neutralizing antibodies you have, the more protected you are."

But infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security, stresses that the Pfizer-BioNTech vaccine is still protective. "The most important part of the Pfizer study is the fact that two doses are sufficient to protect against severe disease, which is the goal that I am most interested in," he says. "I think that the benefit of providing protection against mild breakthrough is not nearly as valuable as protection against severe disease. It is first and second doses that will spare hospitals' capacity concerns." (Related: What Is a Breakthrough Infection?)

Still, if you haven't yet received a booster shot, Dr. Russo urges you to do so. "We're right in the throes of Delta right now with waning immunity [from the first and second doses], so the booster is extremely important," he says. "But if Omicron is able to outcompete Delta, that third shot will be vital as well."

The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it's possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.