As soon as health officials made it clear that the world would need a booster dose of COVID - 19 vaccine, they needed to know whether people could mix doses of vaccines made by different manufacturers.
In the first study to provide results on such cross-dosing, researchers say that it is safe for people who received one of the three vaccines available in the U.S. to get a booster dose of another — and found early evidence that certain combinations might generate stronger immune responses than others. The study was printed on a preprint server and was not yet peer reviewed, and came the same day that the Food and Drug Administration FDA convened a panel of outside experts to review Moderna s request to authorize a booster shot. The FDA and the Centers for Disease Control have issued an Emergency Use authorization for Pfizer BioNTech's booster, but it is currently reviewing data on safety and efficacy of booster from Moderna and J&J.
For the mix-and-match study, the researchers studied 458 people who were initially immune with Pfizer-BioNTech, Moderna or Johnson&Johnson - Janssen vaccines and then randomly assigned to get one of three booster doses about four to six months later. It was not designed to directly compare immune responses of one booster to another, but rather to give researchers a broad sense of whether overall the antibody responses produced were similar across all three boosters — for example, to see whether people who received Pfizer BioNTech s vaccine had similar immune responses after getting an additional dose of a Pfizer-BioNTech, Moderna or J&J's shot.
In general, people who received a booster of a vaccine that was different from the one they originally received saw antibody increases that were similar to or higher than in those who had received another dose of the same vaccine of their initial shot. People who received the single J&J vaccine experienced higher jumps in levels of neutralizing antibodies after getting a booster dose of the Pfizer-BioNTech or Moderna vaccine, compared to another dose of the J&J vaccine: 50 fold for the former two and 5 fold for the latter. Why, it is unknown if it happens that J&J vaccine relies on a different technology than the ones made by Pfizer-BioNTech and Moderna.
The J&J shot uses an adenovirus vector to deliver human genes to the immune system, which then recognizes it as viral and mounts an attack, while Pfizer BioNTech s and Moderna s vaccines employ a new technology of delivering the mRNA form of SARS-CoV - 2 s genetic material directly. And there is some early evidence that the different technologies can be able to increase T-cell immune responses — some preliminary data suggests, for example, that J&J vaccine may be more effective in quickly boosting T-cell based responses that could be more durable and able to recognize new variants than the move heavily antibody-based responses Moderna and Pfizer-BioNTech generate initially. The FDA will be considering such data as it evaluates booster shots from Moderna and J&J Janssen on Oct. 14 and Oct. 15.
The findings are encouraging because they suggest that it s safe for providers to mix and match doses when it comes to boosters. Public health experts have advocated that everyone who has been immunized against COVID - 19 get a booster shot to combat waning protection from vaccines in the face of the faster-spreading Delta variant, and the ability to get any of the three vaccines will ensure that more people will get the additional shot.