Why COVID boosters weren’t tweaked to better match variants

By LAURAN NEERGAARD
AP Medical Writer

COVID-19 booster shots are an extra dose of the original vaccine, and some experts wonder why they weren’t updated to better match the delta variant. With the extra-contagious delta now the dominant version of the virus, experts say future mutants likely will be its descendants. Vaccine makers didn’t ask to change the recipe for booster doses, saying the original shots still work against delta. But Pfizer and Moderna are testing tweaked formulas. Scientists say it’s important to learn how the immune system reacts to a subtly different booster in case it’s eventually needed.