WASHINGTON >> The Biden administration has decided that most Americans should get a coronavirus booster vaccination eight months after they received their second shot, and could begin offering third shots as early as mid- to late September, according to administration officials familiar with the discussions.

Officials are planning to announce the administration’s decision as early as this week.

Their goal is to let Americans who received the Pfizer-BioNTech or Moderna vaccines know now that they will need additional protection against the delta variant that is causing caseloads to surge across the nation. The new policy will depend on the Food and Drug Administration’s authorization of additional shots.

Officials said they expect that recipients of the Johnson & Johnson vaccine, which was authorized as a one-dose regimen, will also require an additional dose. But they are waiting for the results of that firm’s two-dose clinical trial, expected later this month.

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.

Among other worrisome signals, Biden administration officials are particularly concerned about data from Israel suggesting that the Pfizer-BioNTech vaccine’s protection against severe disease has fallen significantly for elderly people who were vaccinated in January or February.

Some administration officials have viewed Israel as a kind of template for the United States because it started vaccinating its population sooner. Israel has almost exclusively used the Pfizer-BioNTech vaccine, and it has a nationalized health care system that allows it to systematically track patients.

The latest data from Israel, posted on the government’s website today, shows what some experts describe as continued erosion of the efficacy of the Pfizer vaccine over time — both against mild or asymptomatic COVID-19 infections in general and against severe disease among the elderly.

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