said a third dose of their Covid-19 vaccine neutralized the Omicron variant in lab tests, but the two-dose regimen was significantly less effective at blocking the virus.
A third dose increased the antibodies 25-fold compared to two doses in the Omicron variant, the companies said. Still, two doses may be effective in preventing severe disease from Covid-19, they said, because immune cells are still able to recognize 80% of the parts of the spike protein that the vaccine targets.
“Although two doses of the vaccine may still offer protection against serious illness caused by the Omicron strain, it is clear from this preliminary data that protection is improved with a third dose of our vaccine,” said Albert Bourla, Managing Director from Pfizer.
The vaccine trains the immune system to fight the virus by generating soldiers in the immune system called 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 be triggered after infection to help target and clear the virus, preventing more serious illness.
Pfizer and BioNTech said the parts of the virus targeted by the vaccine-induced T cells are mostly unaffected by Omicron.
Pfizer and BioNTech are working on a vaccine specific to Omicron that they hope will be available by March 2022 if the variant becomes mainstream by then. Researchers began work on the new vaccine on Thanksgiving Day, November 25, shortly after Omicron was identified.
The laboratory’s preliminary data come from an analysis of blood samples from vaccinated patients measuring antibodies capable of neutralizing the virus that causes Covid-19, including the Omicron variant. Blood samples were taken three weeks after patients received their second dose, or one month after receiving their third dose.
The number of antibodies generated by a third boost against Omicron is similar to that of two doses against an older strain of the virus, the companies said.
The company’s first findings come a day after scientists in South Africa reported the results of the first lab tests showing a 41-fold reduction in neutralization of Omicron by the Pfizer-BioNTech vaccine compared to version original virus.
However, researchers found stronger antibody responses against Omicron in blood collected from fully vaccinated subjects who 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 considered it to be a “variant of concern”. And it has since been detected all over the world, including the United States.
Researchers have been trying to understand how contagious the new strain is, as well as how well it might escape Covid-19 vaccines and whether it causes serious illness. Some preliminary reports suggest the variant is more contagious but could cause milder disease, although researchers say it’s too early to know.
Pfizer stock rose 0.5% pre-market; BioNTech’s US custodian stocks fell 1%.
Write to Joseph Walker at [email protected]
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