1. Division of Virology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
2. Pandemic Preparedness, Infection and Advanced Research Center (UTOPIA), University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
3. Japan SLC, Inc., Hamamatsu, Shizuoka 433-8114, Japan
4. The Research Center for Global Viral Diseases, National Center for Global Health and Medicine Research Institute, Shinjuku-ku, Tokyo 162-8655, Japan
5. Department of Special Pathogens, International Research Center for Infectious Diseases, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
6. Influenza Research Institute, Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53711, USA