On Monday, an international group of scientists, which included the departing F.D.A. officials, decried the push for boosters. In their review, published in The Lancet, the scientists analyzed dozens of studies and concluded that the world would be better served by using vaccine doses to protect the billions of people around the world who remain unvaccinated.
“Our primary goal here in this pandemic was, first of all, to avoid, to end all preventable deaths,” said Dr. Soumya Swaminathan, chief scientist at the World Health Organization and a co-author of The Lancet review. “And since we have the tools to do that very effectively, we should be using it to prevent deaths around the world.”
To prevent the virus from morphing into even more dangerous forms than the Delta variant — and perhaps into one that evades the immune response entirely — the more urgent need, experts said, is to protect the unvaccinated, both in the United States and elsewhere.
The W.H.O. has asked world leaders to refrain from rolling out boosters at least till the end of the year, with the goal of immunizing 40 percent of the global population. But some high-income countries have already begun offering boosters to their residents, and others may follow their lead.
British scientists on Tuesday recommended giving third doses to adults over 50 and other medically vulnerable people in that country. France, Germany, Denmark and Spain are also considering boosters for older adults or have already begun administering them. Israel has authorized boosters for everyone over age 12 and is already contemplating fourth doses for its population.
In the new study, the Israeli team collected data on the effect of booster shots, based on the health records of more than 1.1 million people over age 60. At least 12 days after the booster, rates of infection were 11-fold lower and of severe disease nearly 20-fold lower in those who received a booster compared with those who had received only two doses, the researchers found.