Pfizer and BioNTech said Wednesday that lab tests suggest three doses of their COVID-19 vaccine were able to neutralize the new Omicron variant of the coronavirus, but two vaccine doses alone were significantly less effective at blocking it.

A booster increased antibodies 25-fold compared with two doses against the Omicron variant, the companies said. "The first line of defense, with two doses of vaccination, might be compromised, and three doses of vaccination are required to restore protection," BioNTech Chief Medical Officer Ozlem Tuereci said at a news conference.

The companies also said they could deliver an upgraded vaccine targeted specifically at the Omicron variant in March 2022 if one is needed. BioNTech said that even if an adapted vaccine were available in March, it wouldn't be broadly available for some time, noting that perhaps 25 million to 75 million doses of the new vaccine would be ready at first, Reuters reported.

Pfizer scientist Kena Swanson also said the company is considering testing two doses of an Omicron-specific vaccine in currently unvaccinated people, according to Reuters.

Moderna and Johnson & Johnson also are testing how their vaccines may hold up against the Omicron variant.

President Joe Biden said Wednesday that the Pfizer booster finding is "very encouraging" although he cautioned, "that's the lab report. There are more studies going on."

BioNTech and Pfizer are the first manufacturers of a COVID vaccine to issue an official update on the efficacy of their shots against Omicron. The findings from the companies' early studies were not peer-reviewed and published in a scientific journal.

Blood samples of the lab tests were collected three weeks after patients received their second dose, or one month after receiving their third dose. In the blood samples, the Omicron variant was neutralized about as effectively as two doses neutralized the older strain of the virus, the company said.

BioNTech and Pfizer said two doses of the vaccine should still protect against severe disease because the vast majority of surface structures on the Omicron spike protein targeted by the T-cells, which typically emerge after vaccination, aren't affected by Omicron's mutations.

Pfizer and BioNTech's early findings are broadly in line with a preliminary study published by researchers at the South Africa Health Research Institute in Durban on Tuesday.

Scientists in South Africa reported findings from early lab tests indicating a 41-fold drop in the ability of the antibodies to neutralize the Omicron variant compared with the original virus.

They concluded that people may be more susceptible to breakthrough Omicron infections after just two Pfizer doses compared with other variants — although they didn't test boosters.

The Omicron variant, first detected in South Africa, was classified as a "variant of concern" by the World Health Organization (WHO) on Nov 26.