FILE - This Wednesday, Dec. 23, 2020 file photo shows a vial of the Moderna COVID-19 vaccine in the first round of staff vaccinations at a hospital in Denver. On Thursday, Oct. 14, 2021, U.S. health advisers said that some Americans who received Moderna’s COVID-19 vaccine should get a half-dose booster to bolster protection against the virus. (AP Photo/David Zalubowski, File)

WASHINGTON (AP) — Federal regulators are expected to authorize the mixing and matching of COVID-19 booster shots this week in an effort to provide flexibility for those seeking to maintain protection against the coronavirus.

The upcoming announcement by the Food and Drug Administration is likely to come along with authorization for boosters of the Moderna and Johnson & Johnson shots and follows the authorization of a third dose for the Pfizer vaccine for many Americans last month. The move was previewed Tuesday by a U.S. health official familiar with the matter who was not authorized to speak publicly ahead of the announcement.

The FDA was expected to say that, especially for the mRNA vaccines from Pfizer and Moderna that have proved most effective against the virus, maintaining consistency in the vaccine course was still preferable. The agency was still finalizing guidance for the single-shot J&J vaccine.

Allowing mixing and matching could alleviate supply issues, make the task of getting a booster simpler for Americans and allow people who may have had adverse reactions to the initial dose to try a different shot.

The move will come after the U.S. said it would recognize mixing and matching of vaccines administered overseas, as was common in Canada and some European countries in the early months of the vaccination campaign, for the purposes of entering the U.S.

Copyright 2021 The Associated Press.