1. From the National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta (D.C.D.); and the Department of Medicine, Massachusetts General Hospital (H.M.H., E.S.S.), the Department of Medicine, Harvard Medical School (H.M.H., E.S.S.), the Bureau of Infectious Disease and Laboratory Sciences, Massachusetts Department of Public Health (K.H.), and the Department of Pediatrics, Boston University Medical Center (K.H.) — all in Boston.