Billions more in profits are at stake for some vaccine makers as the U.S. moves toward dispensing COVID-19 booster shots to shore up Americans’ protection against the virus. How much the manufacturers stand to gain depends on how big the rollout proves to be. U.S. health officials late on Thursday endorsed booster shots of the Pfizer vaccine for all Americans 65 and older — along with tens of millions of younger people who are at higher risk from the coronavirus because of health conditions or their jobs. Officials described the move as a first step. Boosters will likely be offered...