EXPLAINER: What do we know about booster shots for COVID-19?

By CARLA K. JOHNSON
AP Medical Writer

U.S. health officials plan to offer COVID-19 booster shots to vaccinated Americans to shore up their protection amid the surging delta variant and evidence that the vaccines’ effectiveness is declining. The effort could start Sept. 20, pending an evaluation by the Food and Drug Administration and advisers to the Centers for Disease Control and Prevention. Researchers and health officials have been monitoring the real-world performance of the COVID-19 vaccines to see how long protection lasts among vaccinated people. The vaccines authorized in the U.S. continue to offer very strong protection against severe disease and death.