Pfizer says its COVID-19 vaccine is safe and strongly protective in kids as young as 12. The announcement Wednesday marks a step toward possibly beginning shots in this age group before the next school year. Most COVID-19 vaccines being rolled out worldwide are for adults, who are at higher risk from the coronavirus. Pfizer’s vaccine is authorized for ages 16 and older. But vaccinating children of all ages will be critical to stopping the pandemic. In a study of 2,260 U.S. volunteers ages 12 to 15, preliminary data showed there were no cases of COVID-19 among fully vaccinated adolescents compared to 18 among those given dummy shots.