Here’s who really needs the new COVID-19 booster

The new U.S. COVID-19 booster campaign needs a dose of clarity about its goals and limitations. The latest “bivalent” vaccine — retooled to protect against the BA.5 variant — will benefit some more than others. The oldest and most vulnerable citizens are likely to benefit most. Public health officials should aim to protect them through a targeted messaging campaign convincing them to get the shot. Younger people should only be encouraged to get it if they’re more than six months out from their last shot.

But the Centers for Disease Control and Prevention has a broader focus — recommending that everyone over 12 get the booster if they’re more than two months out from their last shot or three months out from an infection. That message is less likely to reach those who need it most.

The situation was simpler during the initial vaccine rollout in 2021. The clinical trial data suggested vaccinations would go a long way toward preventing infection, so getting vaccinated was considered not just a personal health choice but a civic duty. There was broad scientific consensus that widespread vaccination would minimize cases and maybe end the pandemic.

That hope was crushed by the discovery of new variants. But there was still a pretty wide consensus that people should get a first booster, thanks to growing evidence that an extra shot, given months later, would help reduce cases and prevent severe illness.

But expert opinion had splintered last spring. Some wanted to keep boosting everyone every six months or so. The problem was a lack of evidence that repeated boosting would make a substantial dent in cases. The new bivalent BA.5 boosters could reduce the odds of infection, but we don’t know by how much.

“At the end of the day, probably what counts most is the time from the last immunization or infection,” says Alessandro Sette, a professor at the La Jolla Institute of Immunology. He says there’s too much emphasis on the number of boosters people are getting, rather than their timing. For four or six months after infection or a previous booster, your immune system probably isn’t very boost-able.

Sette reiterated what Harvard University immunologist Duane Wesemann once told me: Over the months following an infection or vaccine dose, your immune system is slowly improving the quality of your antibody-making B-cells and generating slight diversity that increases the odds of effectiveness against a new variant. The number of antibodies circulating in your bloodstream can decline, but these B-cells continue to retain the ability to make new ones pretty quickly for about six months.

That’s why infectious disease doctor Monica Gandhi of the University of California, San Francisco, told me she’s been arguing that the recommended interval be six months for healthy people — not the two currently recommended (and in some places, mandated).

In principle, pushing forward a massive fall booster campaign could blunt a winter wave, but COVID-19 waves can’t yet be predictably tied to seasonal changes, and nobody knows whether BA.5 or something else will be behind the next surge. It’s also unknown whether boosting someone earlier than about four months does anything to reduce the odds of infection and transmission.

The other essential question is whether the BA.5 bivalent booster has a significant advantage over the original boosters. Sette says the evidence points that way, as least as long as BA.5 remains dominant. He also told me that he was going to go get his bivalent booster the same day as our interview.

But pediatrics professor and Food and Drug Administration advisory committee member Paul Offit is not planning to get the new booster yet. He called the evidence that the bivalent booster was more protective than the original “underwhelming” and, in an opinion piece for the Wall Street Journal, accused the CDC of overselling it, when it’s most likely to benefit the oldest and most vulnerable.

A more targeted CDC messaging campaign would prioritize the 35% of people over 65 who haven’t been boosted at all as they’d benefit the most. Next would be the over-65s who haven’t been boosted or been infected during the last six months. Even if they already had one booster, there’s now evidence that getting a second booster reduces the risk of death. It’s less urgent to reach the two-thirds of adults ages 18-64 who’ve yet to get a single booster, although they’d also benefit, so long as they haven’t been infected in the last four to six months.

In a way, it doesn’t have to be more complicated than the original rollout, which emphasized certain people needed to be first in line: health care workers, essential workers, then older people, then younger people with health problems, and then everyone else.

This time, public health should also rank people by urgency. Even if the overall uptake numbers stay low, the booster campaign can still save lives if it reaches the right people.