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The US Food and Drug Administration this week is expected to authorize the first updated versions of the COVID-19 boosters since the start of the pandemic.
The new injections are reformulated versions of the Moderna and Pfizer-BioNTech vaccines. They are known as “bivalent” vaccines because they are designed to protect against both the original strain and the highly contagious omicron variant.
Specifically, the vaccines are programmed to target the BA.4 and BA.5 omicron subvariants, which are the dominant strains infecting humans and the most capable of penetrating the immune system.
The hope is that the shots will strengthen people’s declining immunity and provide stronger protection against catching the virus, spreading it, and getting sick with COVID and long-term COVID.
The Biden administration is planning to begin making the new vaccines available after Labor Day to help cushion the impact of what could be another surge in infections this fall and winter.
“This is a really important moment in this pandemic,” Dr. Ashish Jha, White House COVID-19 Response Coordinator. “This is the first major vaccine improvement — the first major change in vaccines — in the last two and a half years.”
But the formulation of the boosters and the process of authorizing them has sparked debate among scientists.
For the first time, the FDA is judging how well vaccines work without results from direct human trials. To save time, the FDA is first evaluating vaccines with tests in mice along with the results of human tests of an earlier version of a bivalent vaccine.
Some experts worry that mouse studies are not very reliable in predicting how well vaccines work in humans.
“It could be problematic if the public thinks the new bivalent boosters are a super-strong shield against infection, and thus increase behavioral risk and expose themselves to more viruses,” says John Moore, an immunologist at Weill Cornell Medicine.
But federal officials defend the decision.
Mouse studies suggest that the new vaccines may be about 20 times more protective against omicron than the original vaccines and about five times more protective than the first attempt to create omicron-specific bivalent vaccines, Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, told NPR in an interview.
“This makes us feel confident that they will do what they are intended to do, which is to produce a good immune response against the BA.4/5 variant, as well as refresh our overall response given the original compound as well of the vaccine,” Marks says.
The decision to rely on mouse studies became necessary after the FDA in June rejected new boosters targeting the original type of omicron, known as BA.1, and instead asked vaccine companies to develop injections of new ones targeting the strains that had replaced it.
Some scientists think it’s possible that the new shots could give people immunity that lasts longer than the original shots, and perhaps even protect against new variants that emerge. But more research is needed to confirm this.
Some experts say that the data from the BA.1 boosters show that any potential improvement could be quite modest at best.
“We want a silver bullet. And the booster has become the silver bullet. And we’re putting all our eggs in the vaccine basket,” says Dr. Celine Gounder, a senior fellow at the Kaiser Family Foundation. “I am very skeptical about how much improvement these vaccines will bring in terms of the immunity of the population and the prevention of serious diseases.”
Gounder also worries that the country has stopped doing anything else to protect people, such as wearing masks and improving ventilation.
But others are more optimistic about the new boosters.
“I personally am very excited about bivalent vaccines,” says Jenna Guthmiller, an assistant professor of immunology at the University of Colorado.
“We really need an updated vaccine to provide protection against current omicron lineage viruses, as well as potentially any future omicron variants,” says Guthmiller. “I think it will be fine.”
After the FDA authorizes the vaccine, Centers for Disease Control and Prevention advisers will meet Thursday and Friday to decide whether to recommend it and who should receive it. CDC Director Rochelle Walensky will then have to sign off on that recommendation.
Some experts say that only people who are at high risk because of their ageg health problems should get another booster since the first vaccines still protect most people against serious diseases. Others say that everyone age 12 and older who has not been infected or has been recently infected should get a new vaccine.
“I would say that anyone who is more than six months from a previous flare-up or a previous infection should go get a boost,” says E. John Wherry, an immunologist at the University of Pennsylvania.
“Any opportunity to get more incentive in the population to increase vaccination uptake will be a positive thing to help us get through this pandemic,” Wherry says.
The Biden administration has purchased more than 170 million doses of the new boosters, which should begin to become available after Labor Day.
It remains unclear how much demand there will be for the new boosters, given that many eligible people have yet to receive their first or second boosters.