FDA set to authorize mix and matching for 3rd COVID-19 booster shots in U.S.

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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 expands for additional shots.

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An upcoming announcement by the Food and Drug Administration is likely to coincide with authorization for boosters for 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 US health official familiar with the matter, who was not authorized to speak publicly before the announcement.

The FDA was expected to say that it was still preferable to use the same brand for boosters, especially for the mRNA vaccines from Pfizer and Moderna that have been shown to be most effective against the coronavirus. The agency was still finalizing guidance for the single-shot J&J vaccine.

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Preliminary results from a government study of different booster combinations found that any type of additional dose improves levels of virus-fighting antibodies, regardless of the brand people previously received. But recipients of the single-dose J&J vaccination had the most dramatic response—a 76-fold and 35-fold jump in antibody levels, respectively, immediately after a Moderna or Pfizer booster, compared to a four-fold increase after a second J&J shot.

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One confusing decision is what Moderna recommends in combination with other brands. Moderna has applied for its boosters to be half of the original dosage, saying that’s a lot for people who have already received two full-strength shots. But the mix-and-match study used additional doses at full strength, and there is no way to know whether half the dose of Moderna Booster would trigger as strong a response in J&J recipients.

Allowing mix-and-match could make the task of getting a booster easier for Americans and allow people who may have had an adverse reaction to the initial dose to try a different shot.

Last week, the US said it would recognize a combination of vaccines administered abroad for purposes of entering the country. The practice was common in Canada and some European countries in the early months of the vaccination campaign.

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AP Medical Writer Lauren Niergaard contributed.

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