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.

READ: Omicron v. delta: Battle of coronavirus mutants is critical

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.

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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.