Federal regulators are expected to authorize the mixing and matching of COVID-19 booster shots this week, but who should do it and when?
Mixing and matching refers to giving a booster dose of a vaccine that's different from the vaccine type that was used for the initial vaccination series.
Here's what we know so far.
When is an announcement expected?
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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.
When would it be OK to mix and match?
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.
Already, guidance from the Centers for Disease Control and Prevention has advised that mixing and matching booster shots for immunocompromised individuals, particularly those who received mRNA vaccines, was allowed in some situations.
"For people who received either Pfizer-BioNTech or Moderna’s COVID-19 vaccine series, a third dose of the same mRNA vaccine should be used. A person should not receive more than three mRNA vaccine doses," the CDC's website states. "If the mRNA vaccine product given for the first two doses is not available or is unknown, either mRNA COVID-19 vaccine product may be administered."
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.
The decision follows a highly anticipated study on “mixing and matching” COVID-19 vaccines found the approach to be safe and effective, though the Moderna and Pfizer-BioNTech vaccines were found to spark a stronger immune system response than Johnson & Johnson.
The National Institutes of Health study, which was released Wednesday and has yet to be peer reviewed, found that people who received the Johnson & Johnson vaccine produced stronger antibody levels after receiving a booster shot made by Moderna or Pfizer, compared to a booster from Johnson & Johnson. Those who were originally vaccinated with the Pfizer or Moderna vaccines and received either company's booster shot produced comparably strong immune responses, the researchers observed.
The findings were presented on Friday to the Food and Drug Administration’s advisory committee. The panel met and recommended the authorization of a booster shot of Moderna and Johnson & Johnson.
The advisers didn't vote on whether that should be recommended but told the government to allow flexibility with boosters, saying there were no safety red flags even if it's not yet clear just how much difference, if any, mixing and matching may make in long-term protection.
“In the real world all these kind of combinations are already happening so I think it’s a matter of some urgency for the FDA to help sort out what is admittedly a complicated and challenging scenario,” said Dr. Ofer Levy of Boston Children's Hospital.