1. aDepartment of Immunization, Vaccines and Biologicals, World Health Organization, 20 Avenue Appia, 27 Geneva 1211 Switzerland.
2. bEmergency Department, Karaman Hayat Medical Centre, Karaman, Turkey.
3. cGlobal Influenza Programme, World Health Organization, Geneva, Switzerland.
4. dNational Institute of Hygiene, Warsaw, Poland.