Country reports
WHO-UNICEF Estimates on Immunization Coverage 1980-2006
Introduction
The review of national immunization coverage has produced figures indicating the status of immunization in each country at the beginning of the new millennium. This will guide national and global efforts to further reduce the morbidity, disability and mortality associated with vaccine-preventable diseases.Background
Since June 2000, the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) has made an annual review of national immunization coverage. Immunization coverage estimates are used for a variety of purposes: to monitor the performance of immunization services at local, national and international levels; to guide polio eradication, measles control and maternal and neonatal tetanus elimination; to identify areas of weak system performance that may require extra resources and focused attention; and as one indicator when deciding whether to introduce a new vaccine. Coverage levels with diphtheria-tetanus-pertussis vaccine (DPT) are considered one of the best indicators of health system performance.Methodology
Estimates of immunization coverage are generally based on two sources of empirical data: reports of vaccinations performed by service providers (administrative data*) and household surveys containing items on children's vaccination history (coverage surveys). For estimates based on administrative data, the immunization coverage is derived by dividing the total number of vaccinations given by the number of children in the target population. For most vaccines the target population is the national annual number of births or number of surviving infants (this may vary depending on countries' policies and the specific vaccine). Immunization coverage surveys are frequently used in connection with administrative data. The Expanded Programme on Immunization (EPI) 30 cluster survey, the UNICEF Multiple Indicator Cluster Survey (MICS) and the Demographic Health Surveys (DHS) are the principal types of surveys used as sources of information on immunization coverage.This review relies on the following data:
Officially reported data by member States to WHO;
The historical database maintained by UNICEF;
National Representative Household Survey Reports (published and unpublished).
* Administrative data are collected through the WHO/UNICEF Joint Reporting Form on Vaccine Preventable Diseases, completed annually by countries.
It is important to distinguish whether data accurately reflect immunization system performance or whether they are compromised and thus present a misleading view of immunization coverage. Officially reported data were compared with independent surveys. Based on the data available, consideration of potential biases, and contributions of local experts, the most likely true level of immunization coverage was determined for each year. An essential part of this review was the consultation and collaboration with national authorities, who were asked to review the draft estimates and provide comments.