But there is inadequate evidence to support boosters for the general, younger population, including most people with underlying medical conditions. The C.D.C.’s list of conditions that make someone eligible for a booster is remarkably long, and few if any of these conditions have been shown to carry any additional risk of severe breakthrough illness. Boosters might help some people on the list, but the overall impact is likely to be small. Many thousands of young people would need to get additional shots to prevent a single hospitalization.
There’s also inadequate data on the safety of third doses. The C.D.C. was honest about that. The advisory committee for the agency said it was unsure how many cases of the heart-inflammation condition myocarditis — the most common serious adverse event in young adults — a third dose might cause. Although the number is unlikely to be high, it’s not clear whether the number of young people who might be helped by a booster is greater than the number who might be hurt. The C.D.C.’s committee presented data on this that was inconclusive, and ran models that were openly based on guesses. We appreciated their transparency on that.
But the second set of recommendations ignore that uncertainty in favor of high-stakes epidemiologic gambling. If more people may be harmed than helped by boosters, that’s a nonstarter for any health intervention. In addition, people still on the fence over getting vaccinated at all may be discouraged by the notion of needing a third dose (data show that around one-third of Covid-vaccine-hesitant people say they would be dissuaded).