The Pfizer-BioNTech COVID-19 vaccine is less effective against the Omicron virus variant than other strains of the CCP virus, the companies said Wednesday, citing interim results from a study they’re running.

Scientists found on average a more than 25-fold reduction in neutralizing antibodies against the Omicron variant compared to the wild type, “indicating that two doses of BNT162b2 may not be sufficient to protect against infection with the Omicron variant,” the companies said in a statement.

Pfizer and BioNTech said Wednesday that laboratory tests suggest that three doses of their coronavirus vaccine offer significant protection against the fast-spreading Omicron variant of the virus.

The companies said that tests of blood from people who received only two doses found much lower antibody levels against the Omicron variant compared with an earlier version of the virus. That finding indicates that two doses alone “may not be sufficient to protect against infection” by the new variant, the companies said.

People who have received two doses of the Pfizer-BioNTech Covid-19 vaccine are likely susceptible to infection from the Omicron variant of the coronavirus, but a third shot restores antibody activity against the virus, the companies said Wednesday.