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More than 34 million Americans age 50 and older could soon be eligible to receive another booster shot, after the Food and Drug Administration said Tuesday it had authorized a new round of the Moderna or Pfizer and BioNTech COVID-19 vaccines for those who want them. 

The Centers for Disease Control and Prevention must also sign off on updated recommendations before providers can begin giving the extra boosters. 

“Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals,” said the FDA’s Dr. Peter Marks said in a statement

So far, only Americans with compromised immune systems have been eligible to receive a fourth shot if they were first vaccinated with the Pfizer-BioNTech or Moderna vaccines, or a third shot if they had initially gotten Johnson & Johnson. 

Americans who are old enough to be eligible will be able to get the second booster as early as four months after their first booster. Immunocompromised Americans ages 12 and older who were boosted will also be able to get another shot.

The FDA said their decision was based on data from health authorities in Israel, showing “no new safety concerns” with a fourth dose of Pfizer and BioNTech’s vaccine. The regulator also said data from “an independently conducted study” showed the Moderna fourth dose found no safety concerns “up to three weeks of follow up after the second booster dose.”  

Pfizer and BioNTech had announced a request on March 15 to roll out second boosters for seniors 65 and older. The companies said they had submitted “two real-world data sets from Israel,” where fourth shots had been rolled out for adults 60 and older. Moderna later said it also filed a request for fourth shots, but for all adults, hoping to “provide flexibility” for federal health authorities.

Both Moderna as well as Pfizer and BioNTech are also pursuing new versions of their vaccines that could be rolled out later this year. The companies hope the revised shots will outperform current formulations that were designed to target the initial “ancestral strain” of the virus. 

But for now, the current round of boosters will draw on the same supply of shots currently deployed for initial vaccinations and boosters.

Federal officials have sought for weeks to separate their deliberations over the “immediate situation” to boost the most vulnerable Americans against a new potential wave of COVID-19 cases and discussions over longer-term decisions on fall boosters for the broader population. 

Tuesday’s move was announced without publicly airing the data before either the CDC or FDA’s outside vaccine advisers. The FDA does plan to convene a meeting of the Vaccines and Related Biological Products Advisory Committee next week on the topic. 

“On April 6, the FDA will have an important meeting – and CDC will participate – on what does a fall booster look like? How will we make decisions about that fall booster? Do we, will we, need that fall booster?” CDC Director Dr. Rochelle Walensky told an event hosted by Columbia University on Monday. 

Though the CDC has touted data suggesting the mRNA vaccines “continued to be highly effective” at averting severe outcomes from COVID-19 during the Omicron wave, the agency also acknowledged the significant uptick — and disparities — in severe Omicron infections. 

CDC data also suggests Johnson & Johnson recipients died at higher rates during the Omicron wave compared to other vaccinated Americans, even among those who had received a booster. 

“I think we’re in a relatively weak position on the sort of policy front around exactly what the data are that are compelling decisions about fourth doses,” Dr. Kate O’Brien, a top vaccines official at the World Health Organization, said at the Columbia event. 

“The gap between the evidence required for regulatory authorization of uses of vaccine and really sound policy decisions about optimization of vaccine programs has always been a gap. It continues to be a gap,” said O’Brien.

Supply of second boosters

The move to expand eligibility for a second booster comes as the campaign to roll out first boosters has slowed for months, down to less than 75,000 additional doses per day.

Overall, the White House estimates that some two-thirds of eligible adults have received a booster shot. More than 34 million Americans aged 50 and older were boosted four months ago, according to CDC data

The Biden administration claims it has enough supply to support fourth doses “for our most vulnerable, including seniors” this spring. 

However, White House officials have also warned publicly for weeks that it had run out of money to buy enough additional boosters for all Americans later this year, or to replace current batches if vaccine makers roll out updated formulations tweaked for new variants. 

Moderna’s executives told investors last week that the firm was “actively preparing” for the possibility it would need to sell its vaccine on the private market in the U.S.

“We just want to be ready because we don’t want to be in a world, obviously, where Americans don’t have access to vaccines in the fall,” said Moderna’s CEO Stéphane Bancel.