'Mixing' COVID-19 vaccines triggers a stronger immune response, preliminary NIH study says

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Giving people a different COVID-19 booster than the vaccine series that they originally received is safe and generates an immune response that is stronger, according to a preprint study conducted by the National Institutes of Health. (At this time, only BioNTech BNTX, -2.80% and Pfizer Inc.'s PFE, +0.70% COVID-19 booster has been authorized for people who were previously vaccinated with that vaccine series.) The preprint, which was published Wednesday in advance of a public presentation set for Friday afternoon, evaluates all three authorized or approved COVID-19 vaccines in the U.S. in 458 participants as part of a "mix-and-match" clinical trial. With the exception of the people who were exclusively vaccinated and boosted with Johnson & Johnson's JNJ, +0.20% shots, all participants reported efficacy rates of at least 90.7%. "These data strongly suggest that homologous and heterologous booster vaccine will increase protective efficacy against symptomatic SARS-CoV-2 infection," the authors wrote. There are, however, some limitations to the research. The study is not randomized, and it also only assessed data available 29 days after the participants received their boosters.