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Three years into the pandemic, it has become evident that COVID-19 isn’t going anywhere, and neither are vaccine boosters.
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 does appear 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 currently know about the bivalent booster and how to decide when — and if — you should get your next shot.
For high-risk people — namely adults 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, so it’s unclear how helpful those antibodies are). 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 for COVID-19, 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 (or monovalent) 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 the age of 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.
For people who are under 50 and 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 age 12 showed that 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 ages 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% 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.
“If you’re young, say you’re 35, 40, you’re otherwise healthy, you’ve already gotten vaccinated and boosted and probably had an infection or two in the past, I think that person is pretty well protected for quite some time,” said Dr. David Ho, a professor of medicine at Columbia University who led one of the antibody studies. “Until more data is available, I would not compel such a person to get an annual vaccination.”
The FDA has suggested that, for most Americans, the booster could be given annually in the fall, like the flu vaccine, and high-risk individuals could still receive multiple doses a year. It’s not clear when or if it will formally recommend this approach.
Lin has unpublished research comparing outcomes by the number of booster doses people receive per year. His data shows that people who average less than one booster a year have higher hospitalization and death rates than people who get one or more doses. There is a much smaller difference between one and more than one booster dose per year. He said this suggested that an annual booster was sufficient for most people; however, for older adults, even the small benefit derived from multiple boosters a year is probably worthwhile.
Based on all of the recent findings, there is consensus that if you are at high risk, getting a vaccine booster at least annually, and possibly more frequently, continues to be valuable. For young, healthy people, though, the decision of when to get a booster, or whether to get one at all, is more individual. The CDC and FDA recommend boosters for everyone, but some experts are less bullish on the idea.
“I think if you haven’t had a booster in the last six months, and if you’re over age 50 or even over age 40, you’re going to get some added protection from winding up in the hospital or even dying,” Topol said. “The case between age 5 and 40 is less strong because those people” are rarely hospitalized.
“The expert opinion is divided on whether young, healthy people should get boosted,” Barouch said. “Everybody agrees that the relative benefit is higher in the people who are at highest risk of disease.”
This article originally appeared in The New York Times.
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