1. Yokohama City Institute of Public Health Yokohama Kanagawa Japan
2. Pandemic Preparedness, Infection, and Advanced Research Center The University of Tokyo Tokyo Japan
3. Research Center for Global Viral Diseases National Center for Global Health and Medicine Research Institute Tokyo Japan
4. Department of Infectious Diseases Yamagata University Faculty of Medicine Yamagata Japan
5. Research Center for Influenza and Respiratory Viruses National Institute of Infectious Diseases Tokyo Japan
6. Influenza Research Institute, Department of Pathobiological Sciences, School of Veterinary Medicine University of Wisconsin‐Madison Madison Wisconsin USA
7. Division of Virology, Institute of Medical Science The University of Tokyo Tokyo Japan