To check the safety of COVID-19 vaccines, scientists look for issues during the testing phase and continue their monitoring as shots roll out. So far, the only serious warning to emerge is a rare risk of severe allergic reactions. The U.S. is using shots from Pfizer and Moderna, while Britain and Europe have authorized those plus the AstraZeneca vaccine. Studies found that common side effects were minor and typical of the immune system revving up. But the vaccines are still being monitored. With more than 52 million doses administered in the U.S., health officials say they haven’t detected a safety problem.
