Pfizer and BioNTech have asked the FDA to approve a new version of its COVID-19 vaccine that targets mutated forms of the coronavirus. Pfizer’s updated shot is based on both the original virus that first emerged in 2019, as well as the BA.4 and BA.5 Omicron subvariants that now account for nearly all U.S. cases. Pfizer submitted its application without completing a new clinical trial, meaning it’s not clear whether the updated vaccine will provide more protection. mRNA vaccines produced by Pfizer and Moderna remain highly effective at preventing severe disease and death from COVID but are much less effective at preventing infection and mild disease.