1. Graduate School of Medicine, Kyoto University; Kyoto Kyoto 606-8501 Japan
2. Osaka Prefectural Institute of Public Health; Osaka Osaka 537-0025 Japan
3. National Institute of Hygiene and Epidemiology; Hanoi Vietnam
4. Institute Pasteur; Nha Trang Vietnam
5. International Vaccine Institute; Seoul Korea
6. Center for Southeast Asian Studies; Kyoto University; Kyoto Kyoto 606-8501 Japan