‘Mix and match’ Covid vaccine boosters are effective, NIH study finds

A highly anticipated study of “mixing and matching” Covid-19 vaccines found the approach to be safe and effective, although the Moderna and Pfizer-BioNTech vaccines were found to spark stronger immune system responses than Johnson & Johnson’s vaccine.

“Mixing and matching” refers to giving a booster dose of a vaccine different from the vaccine type that was used for the initial vaccination series.

The National Institutes of Health study, which was released Wednesday but has yet to be peer reviewed, found that people who received the Johnson & Johnson vaccine produced stronger antibody levels after they got booster shots made by Moderna or Pfizer, compared to boosters from Johnson & Johnson. Those who were originally vaccinated with the Pfizer or Moderna vaccines and received either company’s booster shot produced similarly strong immune responses, the researchers found.

The findings will be presented Friday to the Food and Drug Administration’s advisory committee. The group is meeting Thursday and Friday to consider recommending the emergency use authorization of booster shots of the Moderna and Johnson & Johnson vaccines.

The study, credited to 37 doctors and academics, measured the antibody levels of 458 volunteers two weeks and four weeks after the boosters were administered. The booster shots were given four to six months after the original vaccinations.

People were divided into groups based on their original immunizations and were given one of three boosters made by Pfizer, Moderna or Johnson & Johnson. For instance, those who were originally vaccinated with Pfizer’s two-dose regimen got matching Pfizer boosters or “mixed” boosters from either Moderna or Johnson & Johnson.

Antibody levels in people who were originally vaccinated with Johnson & Johnson’s single shot were about five times higher after they received matching Johnson & Johnson boosters. Those who originally received Johnson & Johnson’s vaccine but were given boosters of either the Pfizer or Moderna vaccines had significantly stronger immune responses, including antibody levels that were more than 50 times higher after the Moderna booster.

E. John Wherry, director of the Institute for Immunization at the University of Pennsylvania, who was not involved with the research, said the findings suggest that boosters of the Pfizer or Moderna vaccines would be best for people who received the Johnson & Johnson vaccine. But, he added, the lower antibody levels measured after the Johnson & Johnson booster do not necessarily equate to worse protection.

“I don’t think this is the end of the story,” he said. “I think this is the beginning of the discussion.”

Wherry added that the most important outcome was that the research demonstrates that it is safe to mix different vaccines and boosters. Further studies will be able to provide more granular information about the performances of different combinations, he said, including the other types of immune responses…