Pfizer and BioNTech said Wednesday that two doses of their COVID-19 vaccine were significantly less effective at neutralizing the Omicron variant in early lab tests, but a three-dose regimen was more effective.

Why it matters: Omicron, which has been labeled a variant of concern by the World Health Organization after being identified by scientists in South Africa last month, has forced vaccine makers to reassess the effectiveness of their vaccines against this specific new form of coronavirus.

• Cases of Omicron have been detected in multiple countries around the world, including the United States.
• While preliminary data from South Africa suggests that the variant can spread faster than other variants of the virus, it's currently unknown if the Omicron is more likely to cause severe disease.

What they're saying: "Sera from individuals who received two doses of the current COVID-19 vaccine did exhibit, on average, more than a 25-fold reduction in neutralization titers against the Omicron variant compared to wild-type, indicating that two doses of BNT162b2 may not be sufficient to protect against infection with the Omicron variant," Pfizer and BioNTech said in a press release.

• "A more robust protection may be achieved by a third dose as data from additional studies of the companies indicate that a booster with the current COVID-19 vaccine from Pfizer and BioNTech increases the antibody titers by 25-fold," they added.
• Pfizer CEO Albert Bourla said lab results suggested that two doses of its vaccine still offer protection against severe disease caused by the Omicron strain.
• The companies said they are confident they could begin producing a vaccine specifically tailored to neutralize the Omicron variant in March 2022 if needed.

The big picture: The lab result comes as the Biden administration is attempting to increase booster uptake to head off the Omicron variant.

• The Centers for Disease Control and Prevention changed its recommendation for booster shots late last month, saying everyone 18 and older now "should" receive a booster dose.
• Moderna too has said that it could prepare an Omicron-based vaccine by early 2022 if its vaccines prove less effective at blocking the variant.

Go deeper: Omicron gives a shot to boosters