1. Department of Paediatric Infectious DiseasesInstitute of Tropical MedicineNagasaki University Nagasaki Japan
2. National Institute of Hygiene and Epidemiology Hanoi Vietnam
3. Khanh Hoa General Hospital Nha Trang Vietnam
4. Influenza Virus Research CenterNational Institute of Infectious Diseases Tokyo Japan
5. Department of Clinical MedicineInstitute of Tropical MedicineNagasaki University Nagasaki Japan
6. Graduate School of Biomedical SciencesNagasaki University Nagasaki Japan
7. Department of PaediatricsNagasaki University Hospital Nagasaki Japan