1. Department of Pediatrics, Jeju National University Hospital, Jeju, Korea.
2. Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands.
3. Department of Preventive Medicine, Korea University College of Medicine, Seoul, Korea.
4. Division of Immunization, Korea Disease Control and Prevention Agency, Cheongju, Korea.
5. Department of Pediatrics, Korea University Anam Hospital, Seoul, Korea.