1. MediCity Research Laboratory and Department of Virology, University of Turku, Kiinamyllynkatu 13, FIN-20520 Turku, Finland1
2. Department of Epidemiology and Health Promotion, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, Finland2
3. Haartman Institute, Department of Virology, PO Box 21, FIN-00014 University of Helsinki, Helsinki, Finland3