1Division of Infectious Diseases, Thammasat University Hospital, Pratumthani, Thailand2Influenza Division, National Center for Immunization and Respiratory Diseases, Atlanta, Georgia3Immunization Safety Office, Division of Health Care Quality Promotion, National Center for Preparedness, Detection, and Control of Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia4Saint Louis University School of Public Health, Saint Louis, Missouri