Pfizer Inc. PFE 0.47% and BioNTech SE BNTX 8.17% 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 still able to recognize 80% of parts of the spike protein that the vaccine targets.
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.
“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 improved with a third dose of our vaccine,” said Pfizer Chief Executive Albert Bourla.
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.
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 preliminary lab data comes from an analysis of blood samples from vaccinated patients measuring antibodies capable of neutralizing the virus causing Covid-19, including the Omicron variant. Blood samples were collected three weeks after patients received their second dose, or one month after receiving their third dose.
The number of antibodies generated by a third booster shot against Omicron is similar to two-doses against an older strain of the virus, the companies said.
The company’s early findings come a day after scientists in South Africa reported findings from early lab tests indicating a 41-fold reduction in the Pfizer-BioNTech vaccine’s neutralization of Omicron than the original version of the virus.
The researchers, however, found greater antibody responses against Omicron in blood taken from subjects who were fully vaccinated and had previously been infected with Covid-19.
Omicron was first identified by scientists in South Africa last month. Since then the World Health Organization has deemed it a “variant of concern.” And it has since been detected around the world, including in the U.S.
Researchers have been trying to understand how contagious the new strain is, as well as how well it might be able to evade Covid-19 vaccines and whether it causes severe disease. Some preliminary reports suggest the variant is more contagious but might cause milder disease, though researchers say it is too early to know.
Pfizer shares rose 0.5% in pre-market trading; BioNTech’s American depositary shares fell 1%.
Write to Joseph Walker at [email protected]
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