GSK plc (LSE/NYSE:GSK) has announced that the FDA has approved the Priorix measles, mumps and rubella (MMR) vaccine for individuals at least 12 months old. Before the FDA approval, Merck & Co.’s M-M-R II was the only MMR vaccine currently FDA approved in the U.S. Merck also has an FDA-approved measles, mumps, rubella and varicella…