1. Department of Pediatrics, Chungnam National University College of Medicine, Daejeon, Korea.
2. Division of Vaccine-Preventable Disease Control and National Immunization Program, Korea, Centers for Disease Control and Prevention, Cheongju, Korea.
3. Department of Preventive Medicine, Chungnam National University College of Medicine, Daejeon, Korea.
4. Department of Pediatrics, Incheon Medical Center, Incheon, Korea.