(AP) — The Centers for Disease Control and Prevention has endorsed COVID-19 booster shots for millions of older or otherwise vulnerable Americans. The move opens a major new phase in the U.S vaccination drive against the coronavirus. A panel of advisers made the recommendation Thursday and CDC Director Dr. Rochelle Walensky signed off on it shortly afterward. The advisers said boosters should be offered to people 65 and older, nursing home residents and those ages 50 to 64 who have risky underlying health problems. The extra dose would be given once they are at least six months past their last Pfizer shot.