1. The expanded programme on immunization: a lasting legacy of smallpox eradication;Okwo-Bele;Vaccine,2011
2. WHO/UNICEF coverage estimates for 1980–2012,2012
3. Global vaccine action plan: monitoring, evaluation and accountability. Secretariat Annual Report 2013,2013
4. Global immunization: status, progress, challenges and future;Duclos;BMC Int Health Hum Rights,2009
5. Disease surveillance and burden,2014