Pfizer-BioNTech's updated booster shot generates a stronger immune response against the omicron subvariants BA.4 and BA.5 compared with the original Covid vaccine, the companies said in a release Friday.
The results are based on blood samples taken from adults one month after they received single doses of the updated booster shot or first iterations of the vaccine.
Pfizer's original vaccine formula, which was first administered to older adults in December 2020, was designed to target the original coronavirus strain. The updated booster shot is designed to target the original virus strain, as well as BA.4 and BA.5, in a single shot.
Pfizer said neutralizing antibodies against BA.4 and BA.5 were about four times higher in adults ages 55 and up who received the updated vaccine compared with adults of the same age who received the original vaccine.
The results, which Pfizer announced in a news release, have not been published in a medical journal or reviewed by outside scientists.
Two independent studies posted online late last month suggested that the updated shots do not offer better protection against the new omicron subvariants than the original vaccines do.
The two studies had not yet been peer-reviewed, and experts said they may have been too small to provide any definitive answers about the effectiveness of the vaccines. Still, because the omicron boosters were authorized without human testing, the research offered scientists an early glimpse at how the updated boosters were performing in the real world.
Pfizer’s release Friday does not answer the question of whether the updated shots are effective against infection or severe illness, said Dr. Ofer Levy, the director of the Precision Vaccines Program at Boston Children’s Hospital.
The "results are better than nothing," Levy said, "but it leaves you thirsting for more."
The new findings may hint that the updated booster is better than the original vaccine, but not by much, said John Moore, a professor of microbiology and immunology at Weill Cornell Medical College.
Pfizer said it has shared the data with the Food and Drug Administration and plans to release it to other health regulators around the world.
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