1. National Influenza Center, Statens Serum Institut, Copenhagen, Denmark
2. Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
3. Department of Infectious Diseases, Rigshospitalet University Hospital, Copenhagen, Denmark*
4. Department of Clinical Microbiology, Herlev Hospital, Copenhagen University, Herlev, Denmark
5. Department of Clinical Biochemistry, North Zealand Hospital, Hillerød, Denmark
6. Department of Pulmonary and Infectious Diseases, North Zealand Hospital, Hillerød, Denmark