A Pfizer-BioNTech Covid-19 booster shot appears to provide strong protection against the omicron variant, while the initial two-dose vaccine may be insufficient to prevent infection, the companies announced Wednesday.

Their findings, along with data from separate lab studies, confirm that the new variant is more skilled at sidestepping immune protection provided by existing vaccines than previous strains, but the extent of its abilities to evade the body’s defenses remains unclear as further studies are still needed, health experts say.

Pfizer and BioNTech said laboratory test results show the third dose of their vaccine provides neutralizing antibodies against omicron comparable to those seen against the original coronavirus and other variants after two doses.

Blood samples from those who received only the primary series of the vaccine, on average, did see a 25-fold drop in antibodies against the new variant. That may indicate that the initial two doses of the vaccine may not be sufficient to protect against infection with omicron, although they may still prevent severe disease, the companies said.

“If these data hold, then these are good signs,” said Ali Ellebedy, an associate professor of pathology and immunology at the Washington University School of Medicine in St. Louis. “It means that on the very least, fully vaccinated individuals … will likely be protected from severe disease.”

As the highly mutated omicron variant, first identified in South Africa, spreads around the globe, scientists are racing to determine how the available vaccines will work against it.

“Three doses against omicron are almost equivalent to the two doses effectiveness we had against the … original variant,” Pfizer CEO Albert Bourla said Wednesday on NBC’s “TODAY” show.

“You may need to go get the third booster faster, and that’s something that the health authorities should consider very carefully and make their recommendations,” he added. “But clearly having two doses compared to nothing protects you way better than having nothing.”

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Currently, the Centers for Disease Control and Prevention urges all adults ages 18 and older to get a booster shot six months after their initial two-dose Pfizer or Moderna series or two months after the single-dose Johnson & Johnson vaccine.

Federal health officials are considering whether a booster shot of an mRNA vaccine should be given earlier than at six months from the second dose, Dr. Anthony Fauci, the White House’s chief medical adviser, told “Andrea Mitchell Reports” on MSNBC.

“We’re going to take a look at what available data we have,” he said. “As you know, the Israelis are doing it at five months. We’re going to try and see. The data that we obviously have is fundamentally related to the six months or more.”

Pfizer is the first vaccine maker to release test results against omicron, although Fauci projected that there’s “no doubt” that a third shot of Pfizer’s or Moderna’s vaccine or a second shot of Johnson & Johnson’s vaccine provide “optimal protection” against the virus.

Pfizer and BioNTech said their findings are preliminary. They were detailed in a news release, and the full data has not yet been made available for other scientists to scrutinize.

According to the companies’ news release, blood samples were tested from people who had received either two or three doses of the vaccine. The samples were collected three weeks after the second dose or one month after the booster.

Lab studies are only one piece of the puzzle. Other data is also needed to determine whether a new vaccine is needed. Scientists need to understand how transmissible the omicron variant is, as well as how sick it makes people. Early data suggests it’s more contagious than the delta variant, but causes milder illness.

“Laboratory data are never fully definitive on the efficacy of the vaccines,” said John Moore, a professor of microbiology and immunology at the Weill Cornell Medical College. “The more definitive answer will come from real-world data on what actually happens to vaccinated people who have received two or three doses.”

Will a significant number of fully vaccinated, but not boosted, people turn up in hospitals, infected with the omicron variant?

“As of now, I’m reasonably optimistic that we will not see this happen,” Moore said.

On Tuesday, a South African research institute also released lab results on how the Pfizer-BioNTech vaccine fared against omicron, showing about a fortyfold reduction in vaccine-induced antibodies that could neutralize the new variant. That study didn’t look at booster shots, however.

Moments after those results were released, researchers from the Karolinska Institutet in Sweden posted their own lab findings, which also found a drop in antibody levels against the new variant.

Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said Tuesday night that it is still unclear whether the variant can evade protection against severe illness as the lab studies only look at one component of the immune system.

He said so-called memory B cells and T cells also play important roles.

If the variant is found to evade protection provided by vaccination in real-world studies, people should get booster shots of an omicron-specific vaccine, he said.

Bourla told “TODAY” that current boosters will maintain protection, but if needed, the company could have a variant-specific shot ready by March.

“If we need a new vaccine, those tests are telling me we will be able to have a very good one if we need one against omicron, because really we’re able with some tweaks to produce way higher results,” he said.

Both Moderna and Johnson & Johnson are expected to release results from their vaccine tests against the omicron variant in the coming days. Academic research institutions are also looking into how well the vaccines work against omicron.

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