The Food and Drug Administration on Tuesday authorized a second booster dose of the Pfizer-BioNTech and the Moderna Covid-19 vaccines for adults ages 50 and older.
People are eligible to get the additional dose at least four months after receiving their first booster, the FDA said in a statement.
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Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, is expected to release a statement signing off on the additional shot shortly.
The FDA has already authorized a fourth shot for immunocompromised individuals.
Tuesday’s decision bypasses the independent panel of experts from both the FDA and the CDC, which have issued recommendations to the agencies throughout the pandemic on whether they should clear additional shots, and if so, for which groups.
The share of people who’ve received their first booster remains low in the United States, with fewer than 50 percent of those who are eligible for a booster having received one, according to data from the CDC.
Officials may have a hard time persuading people to get a second booster — as Covid cases, hospitalizations and deaths remain low, some people feel a lack of urgency and have a reduced fear of the disease, experts say.
In addition, many say the US mishandled the rollout of the first booster shot last year when it authorized the dose in a confusing manner.
The move comes as federal health officials gauge whether an extremely contagious omicron subvariant, known as BA.2, will become a substantial threat in the country as it spreads throughout Europe and other parts of the world.
The subvariant accounts for about 55 percent of the new cases in the country, according to the latest data from the CDC.
Both Pfizer and Moderna asked the FDA this month to authorize a second booster, arguing that an additional booster is now needed because research shows protection from the initial booster wanes after a few months. Pfizer’s request was limited to adults ages 65 and older; Moderna’s was for all adults.
Among the research cited is a study from the CDC, which found that the effectiveness of Pfizer’s and Moderna’s vaccines against hospitalization decreased from 91 percent two months after the initial booster shot to 78 percent after four months. The study included the months of December and January, when the omicron variant was spreading rapidly throughout the US
Experts are divided on whether an additional dose is necessary right now, noting that while protection against infection is relatively low, two doses and a booster still provide a high amount of protection against severe disease, hospitalization and deaths, especially in young, healthy people.
However, many experts noted that a second booster may be needed for certain groups, such as older adults or those with underlying medical conditions, in the future.
Other countries, including Chile, Israel and Sweden, already allow for a fourth vaccine dose for certain vulnerable populations.
John Moore, a professor of microbiology and immunology at Weill Cornell Medical College, said the FDA’s decision to allow second boosters for people as young as 50 “seems excessively cautious” as there isn’t much data to show people under 65 would benefit from the additional shot.
He also questioned the timing, noting that Covid cases and hospitalizations remain at low levels and there’s no indication yet that there will be a surge in cases during the summer months.
“What would then happen if there’s a winter surge? Moore asked. “Would people then be expected to get Dose 5 in the fall? Is repetitive boosting now going to be a national policy?”
Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia and a member of the FDA’s advisory committee, also questioned the agency’s reasoning for including the younger age group.
He also said he worries about the possibility of “immune exhaustion” from frequent boosters. That’s when the immune system doesn’t mount the same kind of antibody response it did with previous shots.
The second boosters use the same formulation and dosage as the initial boosters for adults — 30 micrograms for Pfizer’s and 50 micrograms for Moderna’s.
Both companies said the additional boosters were generally well tolerated by people participating in the trials.
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