Who should get a booster? Studies offer some clarity
Last week, an advisory committee to the Food and Drug Administration unanimously agreed that the vaccine and booster process for COVID-19 needs to be simplified in terms of which version of the shot is offered and when and how often people should receive it. There was less consensus about what that simplified process will look like.
The FDA’S desire to streamline vaccine recommendations is a reflection of just how complicated and confusing they have become.
When the bivalent booster, which targets both the original coronavirus strain and the BA.4/BA.5 omicron subvariants, was rolled out in September 2022, there was little data about how well it would work. But the basis for the decision was relatively clear: The virus is evolving, and so should the vaccine. Over the past few months, as the results of initial studies have come in, the picture has gotten murkier.
The good news is the bivalent booster appears to provide protection against severe infection, which is critical for high-risk individuals. It “is doing a much better job of protection, both for symptomatic infections” and hospitalizations, said Dr. Eric Topol, executive vice president of Scripps Research.
The relative benefit for low-risk populations, who are unlikely to die or be hospitalized from COVID-19, is less clear. There are also questions of how often people should get boosted and how the vaccine should be updated as the virus evolves.
Here’s what we know about the bivalent booster and how to decide when — and if — you should get your next shot:
If you’re high-risk, get a booster
For people who are highrisk — namely adults age 50 and older and people who are immunocompromised or have an underlying condition — the evidence is straightforward: If you haven’t gotten the bivalent booster, you should. Just make sure it’s been at least three months since your last shot or COVID infection.
Supporting this recommendation is data presented by Pfizer and Moderna at the FDA meeting, along with four studies published in January in The New England Journal of Medicine. That research found that people who received the bivalent booster had an increase in antibody levels. This suggests it improved immune defenses against the virus, but it didn’t protect against the new strains as well as it did against the old ones.
The biggest jump was in antibodies that target the original strain of the coronavirus (although that version is no longer circulating). Antibodies that target BA.5, which was the dominant strain last summer and fall, also increased substantially. The smallest boost was seen for antibodies that defend against some of the newer omicron subvariants that have more antibody-evading mutations, such as BQ.1.1 and XBB (the current dominant strain, XBB.1.5, wasn’t circulating when the experiments were conducted).
“There’s a clear step down” in protection as the variants continue to progress, said Dr. Dan Barouch, a professor of medicine at Harvard Medical School, who led one of the studies.
When it comes to protecting against severe disease, the bivalent booster fares well in the real world, research from the Centers for Disease Control and Prevention shows. One study found that it was at least 38% effective at preventing hospitalization, and the more time that had passed since someone’s previous vaccine dose, the more the bivalent booster helped.
Similarly, a second study, focusing on adults 65 and older, found that people who had received the bivalent booster an average of 30 days prior were 73% less likely to be hospitalized than those who’d received only the original vaccine or the vaccine plus the initial single-strain booster an average of nearly a year prior.
However, it’s hard to know whether the added benefit of the bivalent booster was because it increased protection against the omicron subvariants or because less time had passed since people got it. Antibodies wane over time — that’s why the CDC and FDA started recommending boosters in the first place — so it’s not surprising people would be better protected the more recently they’d had a shot.
In either case, Barouch said, “for people at high risk of severe complications of COVID-19, it makes a lot of sense to get boosted because it has shown a reduction of severe disease, at least for a brief period of time.”
The boosters also appear to be safe in an overwhelming majority of cases. Last month, the FDA and CDC issued a joint statement that said there was preliminary evidence the bivalent booster may raise the risk of stroke in adults over 65. However, updated data revealed that it was because the comparison group had fewer strokes than normal, not because the recently boosted group had more.
If you’re low-risk, recommendations are less clear
For those under 50 who don’t have an increased risk of severe disease, there’s more of a debate about whether another shot is worth it. The booster is still effective, but getting it is less critical.
One recent study evaluating the bivalent booster in people over 12 showed it worked equally well in individuals of all ages. The researchers compared how people fared during the three months after they received a monovalent booster (May to August 2022) with the three months after people received a bivalent booster (September to December 2022). They found that the monovalent booster was 25% effective at preventing hospitalization or death, while the bivalent booster was 62% effective.
Although the booster worked for everyone, experts say because older adults are much more likely to be hospitalized for COVID-19, they will experience a greater benefit. “Even if this effectiveness is the same, it’s still more important for older people to get boosted because their absolute risk is higher,” said Danyu Lin, a professor of biostatistics at the University of North Carolina at Chapel Hill who led the research.
A CDC study looking at whether the bivalent booster protects against infection in people aged 18 to 49 was also encouraging. Compared with people who received between two and four doses of the original vaccine, people who got the bivalent booster were roughly 50 percent less likely to have a symptomatic infection from either BA.5 or XBB/XBB.1.5.
However, as with the original vaccine, the bivalent booster slightly increases the risk of myocarditis, inflammation of the heart muscle, in people 18 to 35. As a result, some experts are hesitant to recommend more booster doses to this group.