1. Vaccine-Preventable Diseases and Immunization Programme, World Health Organization Regional Office for Europe, DK-2100 Copenhagen, Denmark
2. Translational Pediatrics and Infectious Diseases, Hospital Clínico Universitario and Universidad de Santiago de Compostela, 15706 Galicia, Spain
3. Division of Country Health Programmes, World Health Organization Regional Office for Europe, DK-2100 Copenhagen, Denmark
4. Azrieli Faculty of Medicine, Bar-Ilan University, Ramat Gan 5290002, Israel
5. Vaccine Preventable Disease Programme, Public Health Wales NHS Trust, Cardiff CF10 4BZ, UK