Researchers to study mixing and matching different COVID-19 vaccines as boosters Researchers are testing new forms of booster vaccines. and last updated 2021-06-03 18:16:32-04 As the country pushes to get more people vaccinated, researchers are now looking at mixing and matching different COVID vaccines as a booster for fully vaccinated people. âWe call it mix and match because weâre looking at people who got any of the three EUA authorized vaccines: the Pfizer, the Moderna, or the Janssen vaccine,â said Dr. Robert Atmar, one of the trialâs principal investigators. âAt least in the current part of the study, weâre boosting each of those three groups with the Moderna vaccine.â