Why do we have to get repeated boosters against new variants of viruses? From just a handful of shots in early childhood, we have managed to beat back #measles and #rubella. The reasons for annual #flushots and #COVIDboosters have to do with the viruses’ evolution and our own immune system’s adaptations, Penn scientists explain. They’re also developing #universalvaccines they hope may give lasting protection. Link in bio for the full story. #flushot #fluvaccine #covidvaccine #mrnavaccine