The booster triggered more antibodies against omicron sublineages BQ.1.1, BA.4.6, BA.2.75.2 and XBB.1 in adults older than 55 compared with a fourth dose of the original vaccines, according to new data released by the company on Friday. Antibodies are a key part of the immune system that block the virus from invading cells.
Pfizer developed its booster against omicron BA.5 at the request of the Food and Drug Administration. BA.5 was the dominant strain of Covid in the U.S. over the summer, but is now fading away as subvariants such as BQ.1.1. start becoming more dominant.
BQ.1.1 and its sibling BQ.1 are causing about 48% of new infections in the U.S. right now, according to data from the Centers for Disease Control and Prevention. BA.5, meanwhile, has declined to about 25% of new Covid cases. BA.4.6 and BA.2.75.2 still make up a very small proportion of new infections, while XBB.1 is not present in significant enough numbers to show up in the data yet.
Antibodies against BQ.1.1 were about nine times higher in people who received an omicron booster, while they were about two times higher in those who received a fourth dose of the original vaccine. Among the emerging subvariants, the omicron booster elicited the strongest immune response against BA.4.6 with antibodies 11 times higher, and the weakest response against XBB.1 with antibodies about five times higher.
The booster triggers the strongest immune response against omicron BA.5, the variant it was designed against, with antibodies increasing 13 times in people older than 55, according to data previously released by Pfizer.
U.S. health officials have said the boosters should provide better protection against the emerging subvariants because they are all omicron and many are descended from BA.5.
Pfizer’s and Moderna’s new boosters target both omicron BA.5 and the original strain of Covid that emerged in Wuhan, China, in 2019. The original vaccines only target the first Covid strain and their effectiveness has declined substantially against infection and mild illness as the virus has evolved over the past several years.