And about that data: Everyone wishes it were stronger. While some regard the research out of Israel as sufficient to back a second booster, Dr. Borio sees methodological shortcomings that limit its usefulness in shaping public policy decisions. “Understandably, these sorts of population-wide observational studies aren’t randomized, they’re not taking place in a controlled environment, and there are many confounders,” she said.
For some, timing considerations also loom large. Right now, coronavirus infection rates in the United States are near two-year lows, though some areas are seeing increases. While there’s concern about a coming wave of new cases spurred by the Omicron BA.2 subvariant, in most cases BA.2 seems to cause relatively mild illness for the vaccinated. Recent Centers for Disease Control and Prevention numbers also suggest that most people who are vaccinated, and especially those who got the first booster, remain well protected against severe disease. Considering that a booster’s impact can be short-lived, some say U.S. authorities should wait a bit longer before pushing out another shot.
“It’s not a question of will I ever need another booster — I think eventually everyone will — but rather is now the time, and for whom?” said Dr. Gili Regev-Yochay, the director of the Infection Prevention and Control Unit at Sheba Medical Center in Israel.
Dr. Regev-Yochay has studied the efficacy of the fourth Covid shot. While she fully supports a first booster for all adults, she said the evidence backing a second booster at this time is shakier when it comes to people who don’t have major risk factors. She also pointed out that parts of the world are still trying to get their hands on first doses of the vaccines. “We should save these resources for people who really need them,” she said.
Some experts say that new variants are certain to emerge, and with them may come a more pressing need for boosters that are formulated to target them. Pushing a second booster now could reduce the public’s willingness to get those later shots.
It’s also a theoretical possibility — though far from certain — that boosting people again might reduce the efficacy of forthcoming vaccines. “When challenged with a variant that is resistant to protection against serious illness and you really do need a variant-specific vaccine, you may be less capable of responding to it,” said Dr. Paul Offit, the director of the Vaccine Education Center at Children’s Hospital of Philadelphia and an adviser to the F.D.A. “I’m over 65 but otherwise healthy, and I’m in no rush to get a fourth dose.”
There are yet more plausible arguments for or against boosters. Some say the prospect of additional shots may dissuade the unvaccinated from getting their first doses (which, it’s worth highlighting yet again, every credible expert supports). Meanwhile, others say that the extra shot could offer protection against long Covid or other infection-related health risks. “These sorts of considerations may all be correct, but they’re also in tension with one another,” said Dr. Robert Wachter, the chair of the department of medicine at the University of California, San Francisco.
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