Pfizer, BioNTech say bivalent booster performs better against BA.5 omicron subvariant

American pharmaceutical company Pfizer and its German partner BioNTech announced Friday that a booster dose of their bivalent COVID-19 vaccine performs better against two circulating versions of the omicron variant, compared with a booster shot of their original vaccine.

According to a joint press release, updated data from a Phase 2-3 clinical trial shows the Pfizer-BioNTech bivalent vaccine produced antibody responses against the BA.4 and BA.5 omicron subvariants that were three- to four-fold higher, compared with the original formula, when measured in adults approximately one month after receiving a booster dose. The safety and tolerability profile of the bivalent booster remains favorable and similar to the original vaccine, Pfizer and BioNTech said.

"As we head into the holiday season, we hope these updated data will encourage people to seek out a COVID-19 bivalent booster as soon as they are eligible in order to maintain high levels of protection against the widely circulating Omicron BA.4 and BA.5 sublineages," Pfizer chairman and CEO Albert Bourla said in a statement Friday. "These updated data also provide confidence in the adaptability of our mRNA platform and our ability to rapidly update the vaccine to match the most prevalent strains each season."

Other smaller studies by independent scientists have suggested there is very little difference between antibody responses produced by the original and updated shots, though both boosted antibody protection.

All of these studies are conducted by taking blood samples from recently vaccinated people and measuring antibodies in a lab. They give us a hint of how well the vaccines might work, but do not tell the full story of their effectiveness. Vaccines are still expected to offer a high level of protection against severe illness.

In late August, the U.S. Food and Drug Administration authorized two updated booster vaccines -- the one developed by Pfizer and BioNTech, and another by American biotechnology company Moderna -- that were designed to be a better match against the BA.4 and BA.5 subvariants. Since then, just over 26 million eligible Americans have received the updated booster shots, according to the Centers for Disease Control and Prevention.

The BA.5 subvariant currently estimated to account for half of all new COVID-19 cases in the United States, according to the CDC, but it's unlikely to remain the dominant viral strain for much longer. Newer versions of the omicron variant, such as BQ.1 and BQ.1.1, are slowly overtaking as a proportion of estimated cases. These subvariants are descendants of BA.5, but it remains unclear how well the bivalent boosters will work against them.

As the world nears its third year of the COVID-19 pandemic and the virus continues to evolve, booster shots are expected to bolster protection against severe illness but not necessarily mild or asymptomatic breakthrough infections.

"These data demonstrate that our BA.4/BA.5-adapted bivalent vaccine works as conceptually planned in providing stronger protection against the Omicron BA.4 and BA.5 sublineages," BioNTech CEO and co-founder Ugur Sahin said in a statement Friday. "In the next step and as part of our science based approach we will continue to evaluate the cross-neutralization of the adapted vaccine against new variants and sublineages. Our aim is to provide broader immunity against COVID-19 caused by SARS-CoV-2, including Omicron and other circulating strains."