1. Polio Eradication Programme, World Health Organization Region Office for Africa, Djoue, Congo
2. Vaccine-Preventable Diseases Programme, World Health Organization Regional Office for Africa, Djoue, Congo
3. Department of Community Medicine, Faculty of Clinical Sciences, Bayero University/Aminu Kano Teaching Hospital, Kano, Nigeria
4. Cochrane South Africa, South African Medical Research Council, Cape Town, South Africa