Why Omicron Boosters Weren’t Tested in People

WIt is understandable that nearly all new COVID-19 cases in America are caused by Omicron BA.4 or BA.5 subvariants. Health officials may be considering switching to another vaccine to safeguard the public.

White House COVID-19 coordinator Dr. Ashish Jha believes the Omicron specific boosters will become available as soon as possible in September if approved by the U.S. Food and Drug Administration and Centers for Disease Control and Prevention. Moderna and Pfizer BioNTech submitted their requests to FDA in late August for Omicron-specific boosters.

But with the fall and winter fast approaching—the seasons when respiratory viruses like SARS-CoV-2 spread even more efficiently, as students return to school and people huddle indoors—getting the booster ready requires a more efficient review and regulatory process. This includes safety and effectiveness data from animals. Not people.

Back in June, the FDA’s panel of independent vaccine experts met to consider switching the country to a new booster that targets Omicron, given how quickly that variant is dominating new infections. At the time, the two largest COVID-19 vaccine makers, Pfizer-BioNTech and Moderna—which both make mRNA-based vaccines—had developed shots against an earlier Omicron variant, BA.1. Panel members decided that the booster shot should be modified to protect Omicron. The next vaccine must also defend against BA.4/BA.5 variants, as they continue to make up almost half of all cases during winter.

The vaccine companies were asked to create a new vaccine that would combine the existing vaccine with Omicron BA.4 or BA.5. The FDA requested data from both firms on the new bivalent vaccines at the end of August in order to grant emergency authorization.

The data on safety and effectiveness of the booster was limited due to the time it took to create the shot. The FDA and CDC have already begun human studies and they will continue even if the FDA or CDC approve the shots. The FDA also plans to review data from animal studies without consulting again its advisory board.

This has divided vaccine experts. Dr. Paul Offit, a member of the advisory committee, says this strategy makes him “uncomfortable” for several reasons. Pfizer BioNTech and Moderna presented data in June regarding their BA.1 booster shot. These were focused on levels of the virus-fighting antibody the vaccine produced. “They showed that the neutralizing antibody titers were between 1.5- and two-fold greater against Omicron than levels induced by a booster of the ancestral vaccine,” he says. “I’d like to see clear evidence of dramatic increase in neutralizing antibodies, more dramatic than what we saw against BA.1, before launching a new product. We’re owed at least that.”

Although human research is more difficult, Offit believes that even a small study of 100 subjects to determine their antibodies levels following a booster BA.4/5 would prove useful. “You can boost people and measure their neutralizing antibodies two weeks later,” he says. This information may also help to set realistic expectations about the Omicron booster. The public might feel it’s a panacea that signals the end of the pandemic, but without any data showing how well the booster will protect people from not only getting sick, there might be unrealistic expectations about what the boost can do. “I get a little nervous, frankly, when I hear this [booster] is going to be miraculous,” Offit says.

Some experts view it differently. Based on the fact that the mRNA vaccines have been administered to millions of people so far, with relatively few safety concerns, and given that the vaccines have been effective in protecting people from getting hospitalized or dying of COVID-19, even during the latest Omicron surges, they argue that changing the strain of virus in the vaccine doesn’t require the same extensive testing that the original shot did. “The totality of evidence is relevant here,” says Dr. Ofer Levy, director of the precision vaccines program at Boston Children’s Hospital, and also a member of the FDA’s vaccine advisory committee. “We are in a situation where we need to pivot as variants emerge, and if we try to be too rigid in our approach, we will always be behind, and not giving the population optimal protection.”

Levy stated that Omicron specific boosters, which the FDA is now considering using contain an array of mRNA targets to both the original and Omicron Ba.4/BA.5, and that data is needed on the safety and efficacy of the vaccine for protecting against hospitalization or death. While the data on this vaccine does come from animals, using that data to decide whether or not to authorize the booster is a matter of “hedging bets.” There is data showing that even vaccinated and boosted people can get mild to moderate COVID-19 disease, because their vaccine-induced protection is waning, so boosting with a shot that is better matched to the Omicron subvariants circulating now is a reasonable bet, even if the data on its efficacy comes from animals and not people. “I think it’s the right decision,” says Levy.

There’s no guarantee that the FDA will authorize the new bivalent vaccines, although all signs point to an authorization that could come in a week or so. Health officials will closely monitor data collected from booster recipients to verify that they have not misled them about safety or efficacy. The next winter’s hospitalization rates will show if the Omicron-specific booster is a good investment.

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