COVID-19 boosters: FDA expected to authorize mix-and-match shots

Federal regulators are expected to authorize the mixing and matching of COVID-19 booster doses this week in an effort to provide flexibility as the campaign for extra shots expands.

The upcoming announcement by the Food and Drug Administration (FDA) is likely to come along with authorization for boosters of the Moderna and Johnson & Johnson shots and follows the OK for 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.

MORE NEWS: Attorney: Florida fire battalion chief fired over vaccine reprimand concerns

Preliminary results from a government study of different booster combinations found an extra dose of any type revs up levels of virus-fighting antibodies regardless of the brand people first received.

Recipients of the single-dose J&J vaccination had the most dramatic response -- a 76-fold and 35-fold jump in antibody levels, respectively, shortly after either a Moderna or Pfizer booster, compared to a four-fold rise after a second J&J shot.

Allowing mixing and matching could 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.

MORE NEWS: Nikolas Cruz set to plead guilty to Parkland school shooting

"We're seeing a big decrease in hospitalizations after the booster," FOX News Medical Contributor Dr. Marc Siegel said. "Your chances, if you had the vaccine, even if you didn't have the booster, of getting very sick, getting hospitalized or dying, remains quite low."

However, one confusing decision is what Moderna dose to recommend in combination with other brands. Moderna has applied for its booster to be half the original dose, saying that’s plenty for people who already received two full-strength shots. But the mix-and-match study used full-strength extra doses, and there’s no way to know if a half-dose Moderna booster would trigger as strong a reaction in J&J recipients.

Watch FOX 35 Orlando for the latest Central Florida news.

AP Medical Writer Lauran Neergaard contributed.