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Pfizer said Wednesday that a booster dose of its COVID-19 vaccine may protect against the new omicron variant even though the initial two doses appear significantly less effective.

Pfizer and its partner BioNTech said lab tests showed a booster dose increased by 25-fold the level of so-called neutralizing antibodies against omicron.

Pfizer announced the preliminary laboratory data in a press release and it hasn’t yet undergone scientific review. The companies already are working to create an omicron-specific vaccine in case it’s needed.

Scientists have speculated that the high jump in antibodies that comes with a third dose of COVID-19 vaccines might be enough to counter any decrease in effectiveness.

Antibody levels predict how well a vaccine may prevent infection with the coronavirus but they are just one layer of the immune system’s defenses. Pfizer said two doses of the vaccine may still induce protection against severe disease.

“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 maximized with a third dose of our vaccine,” Pfizer CEO Albert Bourla said in a statement.

Pfizer’s announcement had an immediate impact on U.S. markets. Futures that had pointed to a lower open reversed course in seconds and swung solidly to the positive with the Dow jumping almost 200 points.

‘If you’re concerned … go get your booster’

Doctors studying the variants in Colorado say the news was no surprise but stressed nearly all COVID-related hospitalizations in the state are still from delta.

“We don’t know if omicron is going to out-compete delta,” UCHealth Dr. David Beckham said, “but we definitely know if you get this booster, we think you’re going to be protected. So if you’re concerned, I’d say go get your booster, and your level of concern will be significantly reduced.”

Beckham has been studying the variants in a biosafety lab on the University of Colorado Anschutz Medical Campus. He said the mutations on the omicron variant are allowing it to “sidestep” immune protections more than other variants.

“Omicron has multiple mutations and a lot more mutations than any other variants that we’ve seen so far,” he said. “So for example, delta has a handful, six or so in this spike protein, and omicron has about 30.”

He said there’s also concern that monoclonal antibodies, now being widely used to treat COVID-19 patients, will be less effective should omicron become the dominant variant.

“Because of all the mutations in this omicron variant, there is significant concern that these current monoclonal antibodies we’ve been working to treat our patients, may not work,” he said.