1. Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China
2. Department of Biostatistics, University of Michigan, Ann Arbor, Michigan, USA
3. Chinese Academy of Sciences (CAS) Key Laboratory of Pathogenic Microbiology and Immunology, Center for Influenza Research and Early-Warning (CASCIRE), Institute of Microbiology, Beijing, People's Republic of China
4. School of Public Health (Shenzhen), Sun Yat-sen University, Guangdong, People's Republic of China
5. School of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK