More than 6 million Americans have already gotten a COVID vaccine booster

As the race to fully vaccinate a majority of Americans is still underway, some 6.3 million people, or about 3.4% of fully vaccinated people have already received a third dose.

Fifty-five percent of Americans have been fully vaccinated, according to Our World in Data, but since the FDA authorized a booster shot of the Pfizer-BioNTech vaccine for a narrow eligible group in late September, many people have rushed to get the third shot.

As of Wednesday, an average of 384,963 booster shots are being given daily, while about 281,303 people are initiating the vaccination process every day and about 292,927 people are becoming fully vaccinated daily, according to CDC data as of Wednesday.

The shot is limited to adults older than 65, people at high risk of severe disease, and people whose jobs put them at risk of infection, but with evidence emerging that immunity from two shots of the Pfizer-BioNTech vaccine wanes significantly within months, some have been jumping the line for the jab. Although immunity from catching COVID decreases in the months after receiving the vaccine, protection against hospitalization and severe illness remains high many months afterwards, according to two studies published in the New England Journal of Medicine.

While the Biden administration has been pushing for a broader booster shot push, some medical experts and advisers to the administration have said its plans should be scaled back, according to Politico. Opponents of a broader booster campaign say the priority for vaccination should be on unvaccinated individuals, rather than those who have already been fully vaccinated.

U.S. regulators are studying whether it is safe and effective to take a booster different from the vaccine one originally took, Biden’s chief medical adviser Anthony Fauci told Bloomberg Wednesday. A study of this mixing and matching has already been conducted, and the results are being evaluated, Fauci said. The FDA’s vaccine advisory committee will meet Oct. 14 and 15 to discuss the results, according to a press release published by the agency.

Giving Americans the ability to mix and match vaccine doses safely would greatly expand any efforts to distribute booster shots to the population. Although the Pfizer-BioNTech vaccine is the only one to be approved for a third dose, both Moderna and Johnson & Johnson are seeking approval for a booster, according to the New York Times.