“You have to show some evidence in people that the immune response that you’re getting with the bivalent vaccine is clearly better, and those data haven’t been presented,” said Offit, an infectious disease and vaccine expert at Children’s Hospital of Philadelphia.
“You can’t ask millions of people to get this booster dose without showing some human data that you have a dramatic increase in neutralizing antibodies to the BA.4/BA.5 strains as compared to boosting with the ancestral type,” Offit said, referring to the currently authorized shots based on the version of Covid that emerged in Wuhan, China, more than two years ago.
Michael Osterholm, a leading epidemiologist at the Center for Infectious Disease Research and Policy in Minnesota, also said more data needs to be presented on how the BA.4/BA.5 shots perform in humans.
“It’s not that I don’t think it could work,” Osterholm said. “But I think we need the data first to show that the immune response to this vaccine is equivalent to or better than what we have already.”
Dr. Peter Hotez, an infectious disease and vaccine expert at Baylor College of Medicine in Texas, said it’s worth waiting a little longer for human data on the omicron shots. Hotez led a team that developed a Covid vaccine based on protein technology that is authorized in India.
“I would be surprised if the FDA would move forward on the whole show just based on mouse data alone,” Hotez said. “It’s just a matter of a few extra weeks to get essentially human data. I think it’s worth it because remember, the American people are not rushing to get boosted anyway,” he said.
Omicron BA.5 is the dominant strain of Covid circulating in the U.S. right now, making up about 90% of new infections, according to the Centers for Disease Control and Prevention. The omicron BA.4 and BA.4.6 subvariants represent a little more than 10% of new infections taken together. These versions of omicron are more contagious than past variants of Covid.
Pfizer was originally developing a booster that targets the first version of omicron, BA.1, that caused the massive wave of infection over the winter. But omicron has continued to mutate, and the FDA asked the vaccine makers this summer to switch gears and focus on BA.4 and BA.5.