Covid-19 boosters: 5 takeaways from CDC’s big vaccine meeting

Data reviewed by the Centers for Disease Control and Prevention’s vaccine advisory committee on Wednesday suggests benefits to giving Covid-19 boosters to elderly Americans and long-term care home residents — potentially setting up the independent panel to endorse a third dose of Pfizer and BioNTech’s shot for those groups.

The Food and Drug Administration is expected to soon decide whether to authorize the Pfizer-BioNTech booster and for whom. The agency’s own outside advisory committee on Friday recommended allowing a third dose of the companies’ shot for people 65 and older and those at high risk of severe disease. In doing so they bucked the Biden administration’s plans for a broad booster rollout this month.

The CDC panel’s role begins once the FDA authorizes the booster dose. The CDC’s vaccine advisers will refine exactly who is eligible — in this case, that will likely involve defining “high risk.” Those discussions are set to culminate on Thursday afternoon, but only if FDA authorizes the shot by that morning.

Here are five key takeaways from the first day of the CDC vaccine meeting.

The goals of vaccination might be changing

Data from the large clinical trials used to authorize Covid-19 vaccines in the United States suggested they offered strong protection against even mild infection, raising hopes that the shots would confer so-called sterilizing immunity — preventing vaccinated people from spreading the virus.

But over time, scientists have realized that the vaccines’ ability to ward off mild infection is waning, although protection against severe disease and death remains strong overall.

CDC panel member Sarah Long, a pediatrics professor at Drexel University’s College of Medicine, urged her colleagues to differentiate between ensuring the vaccines prevent hospitalizations versus all infection.

“I don’t think there’s any hope that a vaccine, such as the ones we have, will prevent infection after the first maybe couple of weeks that you have those extraordinary immediate responses,” she said.

The elderly show the clearest need for boosters at this point

Antibodies from vaccination decrease over time among all age groups. But vaccine recipients 80 and older develop lower levels of neutralizing antibodies post-vaccination than younger adults do, said Natalie Thornburg, a respiratory virus immunology specialist at the CDC.

That means that older people’s antibodies may drop to undetectable levels faster, at which point their memory immune cells play a larger role in protecting them against Covid-19. But older people also may produce fewer memory cells than younger people whose immune systems are stronger — suggesting that older people would benefit from a third vaccine dose.

Ruth Link-Gelles of the U.S. Public Health Service said current data shows significant drops in the efficacy of both the Pfizer and Moderna shots in people 65 and older in the time the Delta variant has dominated the domestic infection landscape.

But Thornburg cautioned against viewing vaccines’ protection as an on-off switch. “Immunity is not simply a binary” in which individuals are either protected or not against the coronavirus, she said. Most people are able to maintain some level of cellular immunity, which is likely enough to protect vaccine recipients from severe disease even after antibody levels drop off.

Nursing-home residents face special risks, even with a boost

Boosters may not be enough to fully protect residents of nursing homes, according to modeling data presented by Rachel Slayton of the U.S. Public Health Service. While boosters may help reduce the number of cases in long-term care facilities, she said, that depends on their inherent efficacy and on the vaccination coverage among facility staff.

High community transmission will likely lead to more infections in nursing homes because staff can more easily import the virus, Slayton said. It’s unclear whether booster doses could help curb transmission of the virus among vaccinated individuals.

Experts are worried about confusing the public

Members of the CDC’s vaccine advisory committee expressed concerns Wednesday about green-lighting boosters from one brand over others with authorized Covid vaccines available to Americans, noting the potential for public perception and logistical issues. The panel is tasked with recommending to the CDC how the FDA’s vaccine policy should be implemented in real-world settings.

Long suggested that the group wait for more information on so-called mix-and-match doses — the ability to vaccinate someone with one brand’s primary series with the option for a different manufacturer’s booster later — before signing off on just the Pfizer booster, asking “whether we’re willing to panic half the recipients of Moderna.”

“I don’t want to jeopardize anyone,” she said of delaying a booster decision. “At the same time, it’ll be very, very difficult to have a little less than half of the population who would be eligible to receive” a booster if people can only get the brand that matches their initial series.

Moderna has asked FDA to authorize its booster shot, and Johnson & Johnson has begun submitting booster data to the agency with an eye to filing an application.

Amanda Cohn of the CDC urged committee members to consider the recommendations they’re making now as “interim policies” that will change as more data surfaces. The National Institutes of Health is conducting a study on mixing vaccine doses, with results expected later this year.

“This is a rapidly moving target,” she said.

The booster rollout could be messy

Still, there are a number of challenges to approving only one brand’s vaccine for boosting.

Immunocompromised Americans have already been permitted to seek out third doses of the Pfizer or Moderna vaccines because of concerns they may not have mounted a sufficient immune response to the first two shots. While they’ve been told they can receive the other brand’s shot if they can’t access the one they initially got, FDA isn’t expected to allow mixing brands for people outside that category, which could sow further confusion.

More than 98 percent of Americans participating in a CDC safety monitoring program who have gotten additional doses stuck with the same brand they originally received. But it’s unclear how many of those studied actually fell under the CDC’s definition of immunocompromised since patients only have to attest to their eligibility — no doctor’s note required — meaning there are few obstacles keeping people interested in boosters from acquiring them, anyway.

Declining to allow mixing Pfizer and Moderna doses beyond the immunocompromised could make administering boosters in long-term care facilities difficult if residents received different brands, said Molly Howell, an immunization program manager at the North Dakota Department of Health.

“I don’t know that it’s realistic to keep going back with different brands,” she said.

Katherine Ellen Foley contributed to this report.