what's the rationale behind a covid vaccine booster?

israel is prepared to begin declaring the covid-19 “passports” of more than one million vaccinated israelis null and void, after making boosters — third doses — a requirement for full inoculation, the new york times and financial times reported sunday.

some fear the push to boost risks undermining confidence in the shots and that the unvaccinated will see it as evidence covid-19 vaccines aren’t working. “many of my patients are already saying, ‘if we need a third dose, what was the point,’ ” dr. jason goldman, a doctor in coral springs, fla., told the los angeles times.

others say the issue shouldn’t be positioned so much as “booster” shots, but rather that a third shot is about “completing” vaccination. “we may have found ourselves using two shots when we really needed three,” bioethicist arthur caplan has argued.

durability is driving the debate: emerging evidence suggests a “modest waning” in protection against infection, american and british researchers wrote in a recent editorial in the british medical association journal . an extra dose seems entirely prudent for the elderly and those with compromised immune systems, who tend not to mount as robust an immune response to vaccines, they said, “but overstating evidence of waning immunity for the general population has already had important ramifications, including affecting vaccine confidence.”

the u.s., meanwhile, has begun offering boosters amid “chaotic” and confusing messaging, after the head of the centers for disease control and prevention overruled her own board of advisers and granted emergency use authorization of boosters for people in high-risk jobs and those with underlying health conditions, not just the 65-plus. the united kingdom is deploying third doses for britons over 50, to be given at least six months after a second shot of either pfizer or astrazeneca’s covid vaccine. and on monday, the european medicines agency is expected to weigh in on the need for pfizer boosters for the general population, reuters reported.

it’s not known whether there would be an increased risk of myocarditis, or other rare reactions after a booster dose. data from israel, where more than three million have been vaccinated with a third covid shot, suggest fewer side effects such as fatigue, weakness and pain in the injection site after a third dose versus the second, the times of israel reported. the cdc also has not seen evidence of “unexpected patterns” of side effects after a booster dose of an mrna vaccine among more than 12,000 people who have received one.