Pfizer Inc. and BioNTech SE said that a third dose of their Covid-19 vaccine neutralized the Omicron variant in lab tests but that the two-dose regimen was significantly less effective at blocking the virus.
A third dose increased antibodies 25-fold compared with two doses in the Omicron variant, the companies said. Still, two doses may prove effective in preventing severe illness from Covid-19, they said, because immune cells are able to recognize 80% of parts of the spike protein that the vaccine targets.
The results were issued in a press release by the companies, and weren’t peer reviewed and published in a scientific journal.
The findings from the companies’ early study, and one by scientists in South Africa, suggest that three doses will be needed to produce a similar immune response against Omicron as was provided by just two doses in earlier strains of the virus.
It also bolsters the case for repeated and periodic boosters to maintain people’s immune defenses against an evolving Covid-19, the companies said.
“This is very positive news that should make everyone even more motivated to get vaccinated” and get a booster, said Pfizer Chief Scientific Officer Mikael Dolsten.
The companies’ current vaccine will provide a strong defense against Omicron, especially if people get a booster shot, Dr. Dolsten said. The three-dose regimen, he added, could provide stopgap protection against Omicron through the winter and until a new vaccine targeted directly at the variant would be ready if needed.
Pfizer and BioNTech are working on an Omicron-specific vaccine that they hope to have available by March 2022 if the variant becomes widespread by then. Researchers started working on the new vaccine on Thanksgiving Day, Nov. 25, shortly after Omicron was identified.
The vaccine trains the immune system to fight the virus by generating immune-system soldiers known as antibodies, which attach to the virus and prevent it from replicating in healthy cells. The vaccine also produces other immune-system fighters called T cells that can kick in after infection to help target and clear the virus, preventing more serious disease.
Pfizer and BioNTech said that the parts of the virus targeted by vaccine-induced T cells are mostly unaffected by Omicron.
Dr. Dolsten estimated there is a greater than 50% chance that Omicron becomes the dominant strain spreading in the U.S. by the spring, though it is too soon to know with certainty, he said.
Article by Joseph Walker for The Wall Street Journal