The first boosters are likely to go to nursing home residents and health care workers, followed by other older people who were near the front of the line when vaccinations began late last year. Officials envision giving people the same vaccine they originally received. They have discussed starting the effort in October but have not settled on a timetable.

While many outside experts argue there is no proof yet that the vaccines’ protection against severe disease and hospitalization is waning in the United States, administration officials say they cannot afford to put off figuring out the logistics of providing boosters to millions of people until that tipping point is reached. The spotty nature of the nation’s disease-reporting network makes the question of timing even trickier…

Any booster policy decision is fraught, officials said, because the administration does not want to undermine public confidence in what have proved to be powerfully effective vaccines. Nor does it want to overvaccinate Americans when many other countries have yet to even begin vaccination campaigns in earnest, increasing the threat of dangerous new variants that could spread to the United States and evade the vaccines.