1. Consultant Epidemiologist (Independent), 1081 Brussels, Belgium
2. Department of Vaccinology, University of Antwerp, 2000 Antwerp, Belgium
3. Division of Epidemiology, Norwegian Institute of Public Health, 0403 Oslo, Norway
4. National Institute of Public Health-National Institute of Hygiene, 400-791 Warsaw, Poland
5. Department of Infectious Disease Epidemiology, Immunization Unit, Robert Koch Institute, 13086 Berlin, Germany
6. Meningococcal Reference Laboratory, Austrian Agency for Food and Health Safety, 8010 Graz, Austria
7. Vaccine-Preventable Diseases Programme, European Centre for Disease Prevention and Control, 171 83 Stockholm, Sweden
8. School of Social and Community Medicine, University of Bristol, Bristol BS8 2BN, UK
9. Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London WC1E 7HT, UK