WWith nearly all new COVID-19 infections in the US coming from the Omicron BA.4 and BA.5 subvariants, it makes sense that health officials would consider switching to a different vaccine to protect the public.
dr. Ashish Jha, White House Covid-19 Response Coordinator, expects the first Omicron-specific booster to be available by mid-September at the earliest, as the U.S. Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) consent and recommend the recording. In late August, both Pfizer-BioNTech and Moderna filed requests with the FDA for authorization of their Omicron-specific boosters.
But with fall and winter fast approaching — the seasons in which respiratory viruses like SARS-CoV-2 spread even more efficiently, as students return to school and people creep in — getting the booster ready requires a more efficient assessment and regulatory process. And that includes considering safety and efficacy data from animals, not humans.
In June, the FDA’s panel of independent vaccine experts met to consider switching the country to a new booster targeting Omicron, given how quickly that variant dominates new infections. At the time, the two largest COVID-19 vaccine makers, Pfizer-BioNTech and Moderna — both of which make mRNA-based vaccines — had developed shots against an earlier Omicron variant, BA.1. The panel concluded that if health authorities changed the booster shot to target Omicron, the following should protect against the BA.4 and BA.5 subvariants, which would continue to represent nearly all cases into the winter season.
They asked the vaccine manufacturers to develop a new vaccine, a 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.
However, given the short time they had to develop the injection, the data only includes information about the safety and efficacy of the booster in animals. Human studies are planned and will continue even if the FDA and CDC decide to approve the injections and the government begins to distribute them. The FDA has also decided to review the animal study data without consulting its advisory committee again.
That has divided vaccine experts. dr. Paul Offit, a member of the advisory committee, says this strategy makes him “uncomfortable” for several reasons. He notes that the data presented in June by Pfizer-BioNTech and Moderna regarding their BA.1 booster injection, which targeted the levels of virus-fighting antibodies the vaccine produced, was disappointing. “They showed that neutralizing antibody titers were between 1.5 and two times higher against Omicron than the levels induced 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. We owe that anyway.”
While conducting studies in humans takes more time, Offit says even a small trial of about 100 people to measure their antibody levels after getting a BA.4/5 booster would be helpful. “You can give people a boost 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 feel it’s a panacea that signals the end of the pandemic, but without data showing how well the booster will protect people from not just getting sick, there could be unrealistic expectations about what the boost can do. “I honestly get a little nervous when I hear this” [booster] will be amazing,” says Offit.
Other experts see it a little differently. Based on the fact that the mRNA vaccines have been administered to millions of people to date, 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 the latest Omicron spikes, they claim that changing the virus strain in the vaccine doesn’t require the same extensive testing as the original injection. “The totality of the evidence is relevant here,” says Dr. Ofer Levy, director of the precision vaccine 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 turn when variants arise, and if we try to be too rigid in our approach, we will always be left behind and not protect the population optimally.”
Levy says the latest Omicron-specific boosters the FDA is considering contain a combination of mRNA targets against both the parent virus and Omicron BA.4/BA.5, thus the data on safety and efficacy of the original vaccine to protect against hospitalization and death is relevant. Although the data on this vaccine comes from animals, using that data to decide whether or not to approve 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 as their vaccine-induced protection declines, so it’s a fair guess even if the efficacy data comes from animals and not from people. “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 authorization that could come in a week or so. If the shots are released and people get a boost, health officials will closely monitor the records of those vaccinated to make sure the assumptions they’ve made about the booster’s safety and efficacy hold up. And the hospitalization numbers over the coming winter will show whether betting on the new Omicron-specific booster was the right decision.
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