No mix-and-match trials have yet reported severe side effects. In the Com-COV study, mixing vaccines elicited more side effects than did administering two doses of the same vaccine, according to ...

Mix-and-match COVID boosters are as good as—if not better than—all the same shots Trial was too small to definitively compare combinations, but Moderna may have an edge.

How well do mix-and-match boosters work? The studies of heterologous prime-boosts in Europe earlier this year suggested that mixed vaccines can still deliver good protection against Covid-19.

As boosters are authorized for all three COVID-19 shots available in the U.S., the ability to swap out vaccine types looks to be a boon to the immune system.