COVID-19 vaccine booster shots will become widely available starting on Sept. 20 to Americans who completed the jabs eight months ago.
Department of Health and Human Services announced the measure as infections rise from the Delta variant.
It cited data indicating diminishing protection from the vaccines over time.
The COVID-19 vaccines affected are those made by Moderna Inc, Pfizer Inc and BioNTech AG.
U.S. health officials said they anticipate that people who received the single-dose Johnson & Johnson shot, the other COVID-19 vaccine approved in the United States, will also need boosters.
The United States did not begin administering J&J shots until March.
The booster shots initially will focus upon healthcare workers, nursing home residents and older people, among the first groups to be vaccinated in late 2020 and early 2021, top U.S. health officials said in a joint statement.
There is mounting evidence that protection from the vaccines wanes after six or more months, particularly in older people with underlying health conditions.
The officials cited this in their decision on boosters, but stressed that the U.S.-approved shots have proven “remarkably effective” in reducing the risk of severe disease, hospitalizations and deaths.
The officials included President Joe Biden’s chief medical adviser Anthony Fauci as well as the heads of the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA) and the National Institutes of Health.
“The available data make very clear that protection against SARS-CoV-2 infection begins to decrease over time … and in association with the dominance of the Delta variant, we are starting to see evidence of reduced protection against mild and moderate disease,” the officials said.
In recent weeks, several other countries also have decided to offer booster shots to older adults as well as people with weak immune systems, including Israel, France and Germany.
The United States leads the world in reported COVID-19 cases and deaths. Daily U.S. cases soared from fewer than 10,000 in early July to more than 150,000 in August as the Delta variant took hold.
The new cases include some vaccinated people, though they are far less likely to experience severe disease or death than the unvaccinated.
According to CDC data, more than 72% of Americans 18 and older have received at least one vaccine dose and nearly 62% are fully vaccinated. Of the total population, the CDC said 59.9% have received at least one dose and 50.9% are fully vaccinated.
A study by an Israeli healthcare provider released on Wednesday found that a third dose of the Pfizer/BioNTech shot is 86% effective in people over age 60.
It followed another Israeli study released this week that showed evidence of waning immunity from COVID-19 vaccines in the months after inoculation, raising the risk of serious infection among the elderly and people with compromised immune systems.
