WHO-UNICEF Estimates on Immunization Coverage 2000-2011
IntroductionThe 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.
BackgroundSince June 2000, the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) have conducted annual reviews 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.
A detailed explanation of the methods behind the WHO and UNICEF estimates of national immunization coverage is provided elsewhere*. 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:
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 are compared with independent surveys. Based on the data available, the consideration of potential biases, and the contributions of local experts, the most likely true level of immunization coverage is determined for each country–year–antigen combination. An essential part of this review is consultation and collaboration with national authorities, that are asked to review the draft estimates and provide comments.
The attached graphs and data tables show the national coverage levels for each vaccine for the period from 2000 through 2011 (see guide). Owing to evolving methodology and revisions of the time series, comparisons with previously reported data are not advised.
*1. Burton A, Kowalski R, Gacic-Dobo M, Karimov R, Brown D. A Formal Representation of the WHO and UNICEF Estimates of National Immunization Coverage: A Computational Logic Approach. PLoS ONE. 2012;7(10):e47806.
3. Burton A, Monasch R, Lautenbach B, Gacic-Dobo M, Neill M, Karimov R, Wolfson L, Jones G, Birmingham M – WHO and UNICEF estimates of national infant immunization coverage: methods and processes. Bull World Health Organ. 2009; 87:535–541.
** Administrative data are collected through the WHO/UNICEF Joint Reporting Form on Vaccine Preventable Diseases, completed annually by countries.