The U.S. Food and Drug Administration said Tuesday it has approved the emergency use of an additional dose of coronavirus vaccines separately developed by Pfizer Inc. and Moderna Inc., with people aged 50 or older eligible for the fourth shots. The regulators decided to greenlight the “second booster” for people in the age bracket after finding the fourth shot appears to have been effective in preventing infected people in Israel from developing serious illness, while there are no fresh safety concerns from additional shots. People aged 50 or older who received the booster shot more than four …