WASHINGTON, D.C. (TIP): Federal regulators authorized second booster shots of the Pfizer-BioNTech and Moderna coronavirus vaccines on Tuesday for everyone 50 and older. The move came after the Biden administration decided it should seek to bolster waning immunity in older Americans in case the virus sweeps the nation again in the coming months. The Food and Drug Administration also authorized a second booster dose for individuals at least 12 years old and older with certain immune deficiencies, such as people who have undergone solid organ transplants. The agency said the additional shot can be given at least four months after a first booster for both cohorts.

The Centers for Disease Control and Prevention is expected to issue some kind of advice on who should consider getting the shot as early as Tuesday. As of late last week, officials were planning to present the second booster essentially as an option that older Americans or people with underlying medical conditions should consider.

The F.D.A. made the decision with scant data, as an interim measure to strengthen protection for older Americans and others considered especially vulnerable until the fall. At that point, federal health officials say they expect that everyone will need another shot. There is some hope that by then, scientists will have developed vaccines that work better against the variants that have emerged over the past four months. The idea that another shot is necessary now, just six months after federal regulators authorized the first round of boosters, could add to fatigue with Covid vaccines. With each authorized additional dose, fewer and fewer Americans get the shot.

On the other hand, many experts now acknowledge that the government’s decision last fall to authorize a first booster shot — the subject of much scientific debate at the time — saved lives during the winter Omicron wave.