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FDA ready to bless mixing and matching of COVID-19 vaccines as boosters

Data from a National Institutes of Health (NIH) study on booster shots have convinced the FDA to allow Americans to use a different COVID-19 vaccine for a booster dose than they received for their original vaccination, and a ruling could come this week, The New York Times reports.

Allowing mixing and matching of vaccines would provide more flexibility for providers and those seeking boosters. But it could also ultimately damage booster usage of the Johnson & Johnson vaccine as the NIH data showed that mRNA shots afforded superior immune responses when used as a follow-up dose.

The ruling could also help Moderna sales as the data showed its vaccine elicited slightly higher antibody counts than Pfizer’s when used as a booster. Those who conducted the study were quick to point out its limitations, including the uncertainty of how antibody counts equate to actual protection against the virus.

On Friday afternoon an FDA advisory committee discussed the mix-and-match booster study but did not extend a recommendation.

While some experts at the meeting discussed the need for more conclusive data to be collected over a longer term, others believed the results were convincing enough to recommend the mixing and matching of vaccines as boosters.

“It will be confusing to the public if we now start to consider authorizations for mixed or heterologous vaccines,” Ofer Levi, M.D., of Boston Children’s Hospital, told the panel. “On the other hand, we have to follow the science. We’re still in the pandemic here and if there’s opportunity to offer benefit, that’s our job.”

In the study, investigators split 458 volunteers into three groups depending on which of the three currently authorized vaccines they originally received. Then, within each of those groups, participants split up further into three more groups, with each subgroup receiving a different booster dose four to six months after their original vaccination.

The most significant finding was that J&J recipients who received a second shot of the Moderna or Pfizer vaccine got an antibody surge of 10 to 20 times greater than those boosted with another J&J shot.

The data also showed that those who were originally inoculated with the two-dose primary series from Moderna or Pfizer experienced similar immune responses from either of the mRNA vaccines as boosters. Additionally, those vaccinated exclusively with Moderna shots had slightly higher antibody counts than those who were dosed with Pfizer, either as a primary course or as a booster.

“We just authorized additional doses of vaccines, based on, in the case of Moderna at least, a very small amount of safety data,” said Eric Rubin, M.D., of Harvard Medical School. “Here we have vaccines that are safe. We have modalities that we understand for delivering those vaccines. I’m pretty comfortable that with a relatively small sample size that we can be certain of safety.”

Recent reports show that some Americans are already convinced of the interchangeability of the vaccines as some people who are eligible have received a booster dose of the Pfizer vaccine, regardless of which shot they originally received.

“Many Americans are taking matters into their own hands,” Levy said Friday. “It’s a matter of some urgency for FDA to help sort out what admittedly is a complicated and challenging scenario. But we can’t hide from it and I do think we need to give guidance to the public.”

Last week, the advisory committee recommended approval of a half dose of the Moderna vaccine as a booster for those age 65 and older and others who are at high risk. The committee also recommended a second dose of the Johnson & Johnson vaccine for those age 18 and older two months after their original vaccination.