The new US Covid booster campaign needs a dose of clarity about its goals and limitations. The latest “bivalent” vaccine — retooled to protect against the currently circulating 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.
Right now, however, 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 diffuse 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 that vaccinations would go a long way toward preventing infection in the first place, and so getting vaccinated was considered not just a personal health choice but a civic duty for everyone. There was broad scientific consensus that widespread vaccination would minimize cases and maybe even end the pandemic.
That hope was crushed by the discovery of immunity-evading 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 by the spring of 2022. Some wanted to keep boosting everyone every six months or so, either with the original vaccines or with updated boosters. The problem was a lack of evidence that repeated boosting would make a substantial dent in cases. The new bivalent BA.5 boosters could plausibly 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 right now there’s too much emphasis on the number of boosters people are getting, rather than their timing. For two or three months after infection or a previous booster, your immune system probably isn’t very boost-able. There might be some benefit after three months, but, he says, you’d get the most benefit after four-to-six months.
Sette reiterated what Harvard University immunologist Duane Wesemann told me for a previous column: 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 University of California, San Francisco infectious disease doctor Monica Gandhi 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 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. In fact, Sette told me that he was going to go get his bivalent booster that same day, right after our interview was over.
But pediatrics professor and Food and Drug Administration advisory committee member Paul Offit is not planning to get the new booster just yet. He called the evidence that the bivalent booster was more protective than the original “underwhelming” and, in an opinion piece for the WSJ, 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; they’d benefit the most from the retooled booster. Next on the priority list 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, so a second shot is worth it. It’s less urgent to reach the two-thirds of adults aged 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 around, public health should also rank people by urgency, starting with unboosted people over 65. Even if the overall uptake numbers stay low, the booster campaign can still save lives if it reaches the right people.