In this Wednesday, March 24, 2021 image from video provided by Duke Health, Alejandra Gerardo, 9, looks up to her mom, Dr. Susanna Naggie, as she gets the first of two Pfizer COVID-19 vaccinations during a clinical trial for children at Duke Health in Durham, N.C. In the U.S. and abroad, researchers are beginning to test younger and younger kids, to make sure the shots are safe and work for each age. (Shawn Rocco/Duke Health via AP)
