Omicron boosters are coming but not tested on humans

Usince almost all new COVID-19 infections in the US come from the Omicron BA.4 and BA.5 subvariants, it makes sense for health officials to consider switching to another vaccine to protect the public.

White House COVID-19 Response Coordinator Dr. Ashish Jha expects the first Omicron-specific booster will be available as early as mid-September if the US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) authorize and recommend the vaccine. At the end of August, both Pfizer-BioNTech and Modern submitted requests to the FDA for authorization of their Omicron-specific boosters.

But as fall and winter approach — the seasons when respiratory viruses like SARS-CoV-2 spread even more effectively, as students return to school and people huddle indoors — booster preparations require a more effective review and regulatory process . And that includes looking at safety and efficacy data from animals, not humans.

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 dominates new infections. At the time, the two largest makers of COVID-19 vaccines, Pfizer-BioNTech and Moderna – both of which produce mRNA-based vaccines – had developed vaccines against an earlier variant of Omicron, BA.1. The panel decided that if health authorities were to change the booster shot to target Omicron, the next one should protect against the BA.4 and BA.5 subvariants, which will continue to account for almost all cases in the winter season.

They asked vaccine manufacturers to develop a new vaccine that combined the original vaccine and also targeted Omicron BA.4 and BA.5. In late August, both companies submitted data on their new bivalent vaccines to the FDA for emergency use authorization.

Given the short time they had to develop the injection, however, the data only included information on the safety and efficacy of the booster in animals. Human studies are planned and will continue even if the FDA and CDC decide to allow the injections and the government starts distributing them. The FDA also decided to review the animal study data without consulting its advisory committee again.

This divides vaccine experts. Dr. Paul Offitt, a member of the advisory committee, says this strategy makes him “uncomfortable” for several reasons. He noted that data presented by Pfizer-BioNTech and Moderna in June involving their BA.1 booster shot, which focuses on the levels of virus-fighting antibodies generated by the vaccine, were disappointing. “They showed that neutralizing antibody titers were between 1.5 and 2 times higher against Omicron than the levels elicited by a booster of the ancestral vaccine,” he says. “I would like to see clear evidence of a dramatic increase in neutralizing antibodies, more dramatic than what we saw against BA.1, before we launch a new product.” At least that’s what we’re owed.”

Although conducting human studies does take more time, Offit says that even a small trial involving about 100 people to measure their antibody levels after receiving a BA.4/5 booster would be useful. “You can boost people and measure their neutralizing antibodies two weeks later,” he says. Such information can also be critical in setting realistic expectations for the Omicron booster. The public may think it’s a panacea that signals the end of the pandemic, but without any data showing how well the booster will protect people from more than just disease, there may be unrealistic expectations of what the booster can do. “I get a little nervous, to be honest, when I hear that [booster] it will be a miracle,” Offit says.

Other experts see it a little differently. Based on the fact that 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 hospitalization or death from COVID-19, even during of the latest Omicron jumps, they argue that changing the virus strain in the vaccine does not require the same extensive testing as the original injection. “The body of evidence is important here,” said Ofer Levy, MD, 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 have to pivot as options arise, and if we try to be too rigid in our approach, we will always fall behind and not provide the population with optimal protection.”

Levy says the latest Omicron-specific boosters the FDA is considering contain a combination of mRNA targets against both the original virus and Omicron BA.4/BA.5, so the safety and efficacy data from the original vaccine to protect against hospitalization and death is relevant. Although the data for this vaccine come from animals, using this data to decide whether or not to allow the booster is a matter of “hedging bets.” There are data to show that even vaccinated and boosted people can get mild to moderate disease from COVID-19 as their vaccine-induced protection wanes, so boosting with a vaccination that is better matched to the currently circulating sub-variants of Omicron, is a reasonable bet, even if the data on its efficacy come from animals, not humans. “I think it’s the right decision,” Levy says.

There is no guarantee that the FDA will approve the new bivalent vaccines, although all signs point to an approval that could come in about a week. If the vaccinations are released and people are boosted, health officials will closely monitor the data from those vaccinated to ensure that the assumptions they made about the safety and efficacy of the booster hold. And next winter’s hospitalization rates will reveal whether committing to the new Omicron-specific booster was the right decision.

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