1. Virus Research & Development Laboratory Statens Serum Institut, Copenhagen, Denmark
2. Public Health Agency of Sweden, Solna, Sweden
3. National Influenza Centre Norway, Norwegian Institute of Public Health, Oslo, Norway
4. Department of Molecular Medicine, University of Padova, Padua, Italy
5. Department of Microbiology, Oslo University Hospital, Oslo, Norway
6. Karolinska Institutet, Solna, Sweden
7. Infectious Disease Research Unit, University of Southern Denmark, Odense, Denmark