Pfizer says kid-size doses of its COVID-19 vaccine are safe and nearly 91% effective at preventing infections in elementary school children. Details of the study were posted online Friday as U.S. regulators consider opening vaccinations to youngsters 5 to 11. The shots could begin early next month if regulators give the go-ahead. If the FDA authorizes the low-dose shots, the Centers for Disease Control and Prevention will make the final recommendations on who should receive them. Full-strength Pfizer shots already are authorized for anyone 12 or older.