Affiliation: | 1. Department of Pediatrics, Sapporo Medical University School of Medicine, Sapporo, Japan;2. Department of Public health, Sapporo Medical University School of Medicine, Sapporo, Japan;3. Hokkaido Medical Center for Child Health and Rehabilitation, Sapporo, Japan;4. Department of Virology Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan |