Q&A on Omicron-Updated COVID-19 Boosters

Earlier this month, the U.S. began administering the first COVID-19 booster vaccines that have been updated to better match the latest circulating coronavirus strains.

Many scientists expect the revised boosters will be more effective than their predecessors, but whether that’s the case and to what degree remains unknown.

The new vaccines, from mRNA vaccine makers Pfizer/BioNTech and Moderna, are bivalent, meaning that along with the original version of the coronavirus, or SARS-CoV-2, they also specifically target the BA.4 and BA.5 omicron subvariants. At the end of August, the Centers for...