“I very strongly believe that we need a vaccine for adolescents and children, but I want to be sure that the risk of the vaccine is lower than the risk of hospitalization” from covid-19, said H. Cody Meissner, an infectious-diseases physician at Tufts Medical Center, noting that vaccines can carry risks and young children have a very low risk of being hospitalized. “As we generate herd immunity, this disease is disappearing, between the vaccine and natural immunity.”