Study finds ‘mixing and matching’ boosters safe, but Moderna, Pfizer are best

Receiving a booster dose of a different vaccine than what was initially administered is safe and effective, though people who received Johnson & Johnson’s vaccine may get more benefit from a booster of an mRNA vaccine such as Pfizer’s or Moderna’s, according to data released Wednesday.

A highly anticipated preprint study on “mixing and matching” vaccines from the National Institutes of Health found that boosting with any of the three vaccines currently licensed or authorized for emergency use in the U.S. will generate an immune response.

However, people who received a booster dose of either the Moderna or Pfizer vaccines had a higher increase in their antibody responses more often than those who received an extra dose of J&J, according to the study, which has not yet been peer reviewed.

The data from the study will be presented to an outside advisory panel of the Food and Drug Administration later this week as part of a series of meetings to consider requests from both Moderna and J&J to authorize booster doses of their vaccines.

The study followed 458 volunteers and measured their antibody levels two weeks and four weeks after the boosters were administered. The booster shots were given four to six months after the original vaccinations.

Those who initially got the two-dose Moderna vaccine got either another Moderna shot, a Pfizer shot or a Johnson & Johnson shot as a booster four to six months after their primary immunization.

Scientists have hypothesized that mixing different vaccines may give people broader protection against the coronavirus and new variants, as well as simplify the logistics of administering booster vaccines.  

Broadly, people who received an mRNA-based booster vaccination had a four-fold increase in their neutralization response more frequently than those who were boosted with J&J’s adenovirus vaccine.

A booster dose of Moderna’s vaccine provided the highest boost of neutralizing antibodies in people who received any of the other vaccines as the primary dose.

People who received Moderna’s vaccine as the prime dose had higher levels of neutralizing antibodies even prior to a booster — about three times higher than Pfizer and 10 times higher than Johnson & Johnson. 

But the increase in immune response of a Moderna booster compared to a Pfizer booster was likely not significant enough to make a noticeable difference. Also, the researchers tested full doses of all the vaccines, rather than the half-dose that Moderna requested authorization for in its booster.

Some experts have also suggested not dismissing the small level of protection gained from a booster of J&J’s vaccine found in the study, because there’s a chance antibody levels could continue to rise with more time. 

The study also measured antibody levels, which does not necessarily equate to whether someone gets infected.