1Division of Infectious Diseases, Department of International Health, Kobe University Graduate School of Health Sciences, 7-10-2 Tomogaoka, Suma-ku, Kobe 654-0412, Japan, E-mail: yamato.t@yahoo.com
2Division of Vaccinology, Department of Microbiology and Infectious Diseases, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650- 0017, Japan, E-mail: yamato.t@yahoo.com