Noni MacDonald1, Eve Dubé2, Robb Butler3. 1. Department of Paediatrics, Dalhousie University, Canadian Centre for Vaccinology, IWK Health Centre, Halifax, Canada. 2. Institut national de santé publique du Québec, Centre de recherche du CHU - Université Laval, Québec, Canada. Electronic address: Eve.Dube@inspq.qc.ca. 3. Division of Health Emergencies and Communicable Diseases, WHO Regional Office for Europe, Copenhagen, Denmark.