The U.S. Food and Drug Administration (FDA) is expected to allow the mixing and matching of COVID-19 vaccine booster doses this week, according to reports.

The forthcoming announcement by the agency is anticipated as the campaign for additional shots continues and as more Americans head back for a third jab. 

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The Associated Press reported on Tuesday – citing an anonymous U.S. health official familiar with the matter – that the news would likely be put out alongside the authorization for boosters of the Moderna and Johnson & Johnson shots, though the FDA was still predicted to say that using the same brand for a booster was the preferable option and especially for mRNA vaccines from Pfizer and Moderna.

The FDA declined to comment.

Last month, regulators OK'd a third dose for the Pfizer/BioNTech vaccine for many Americans and last week the U.S. said it would recognize combinations of vaccines administered overseas for the purpose of entering the country.

In this March 3, 2021 file photo, a vial of the Johnson & Johnson COVID-19 vaccine is displayed at South Shore University Hospital in Bay Shore, N.Y.

In this March 3, 2021 file photo, a vial of the Johnson & Johnson COVID-19 vaccine is displayed at South Shore University Hospital in Bay Shore, N.Y. (AP Photo/Mark Lennihan, File)

While receiving a different COVID-19 vaccine booster from the one initially received could simplify the booster process – in addition to allowing those with adverse reactions to the initial dose to try a different shot – questions remain.

Moderna has applied for its booster to be half of the original dose, but a National Institutes of Health study of booster combinations used full-strength extra doses. 

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Preliminary results found that an extra dose of any type increases the amount of virus-fighting antibodies, with recipients of the single-dose Johnson & Johnson vaccination showing the most remarkable response. 

The New York Times reported Tuesday that vaccine providers could also use their discretion to offer a different brand.

The newspaper said that the FDA was projected to authorize the Moderna and Johnson & Johnson boosters by Wednesday night and that a U.S. Centers for Disease Control and Prevention (CDC) advisory committee would take up the topic on Thursday before issuing its own recommendations. 

The Times said that officials are expected to authorize a booster of Moderna's vaccine about six months after the second shot and a Johnson & Johnson booster would be allowed at least two months after the first dose.

They also pointed out that the mix and match study's researchers warned against using findings to conclude that any single combination of vaccines was better than the others.

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All of this comes after lengthy deliberation about the need for boosters shots at all, as vaccines in the U.S. remain effective against hospitalization and death from the virus and its delta variant.

More than 189 million Americans are fully vaccinated, according to CDC data.

The Associated Press contributed to this report