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Article Excerpt
Introduction
WHO recommends that all children receive one dose of bacille Calmette-Guerin vaccine (BCG), three doses of diphtheria--tetanus-pertussis vaccine (DTP), three doses of either oral polio vaccine (OPV) or inactivated polio vaccine (IPV), three doses of hepatitis B vaccine, and one dose of a measles virus-containing vaccine (MVCV), either anti-measles alone or in combination with other antigens. (1-9) It also recommends three doses of vaccine against infection with Haemophilus influenzae type b (Hib). (10) To boost immunity at older ages, additional immunizations are recommended for healthcare workers, travellers, high-risk groups and people in areas where the risk of specific vaccine-preventable diseases is high. (11)
Immunization coverage levels and trends are used (i) to monitor the performance of immunization services locally, nationally and internationally; (ii) to guide strategies for the eradication, elimination and control of vaccine-preventable diseases; (12-14) (iii) to identify areas of immunization systems that may require additional resources and focused attention; (15,16) and (iv) to assess the need to introduce new vaccines into national and local immunization systems. (17) Models of vaccine-preventable disease burden frequently include immunization coverage levels among their components. (18-20) Coverage levels for measles vaccine and DTP are indicators of health system performance frequently considered by funding agencies when reviewing applications for financial and technical support. (21-24) Measles immunization coverage is one of the indicators for tracking progress towards Millennium Development Goal 4, to reduce child mortality. (25) Furthermore, trends in immunization coverage are used to establish the link between immunization service delivery and disease occurrence and to provide a framework for setting future coverage goals. (26)
Trends in immunization coverage
While some countries had routine immunization systems in place before 1980, major national and international development of routine, universal infant immunization systems did not begin until the late 1970s. In fact, it was not until the 1980s that dramatic improvements in immunization coverage were achieved, along with an increase in coverage with the third dose of DTP vaccine (DTP3) from 20% in 1980 to 75% coverage in 1990. While some countries reported significant declines in coverage after 1990, global coverage levels remained fairly constant and began rising slowly but steadily in 2000, until DTP3 coverage worldwide had reached 81% in 2006.
In 1980, fewer than 10% of the world's children lived in 20 of the 167 countries with DTP3 coverage levels greater than 80%; 84% of the world's children lived in countries where coverage was less than 50%. By 1990, 108 countries (43% of all children) had DTP3 coverage levels greater than 80%, and fewer than 10% of children lived in countries with under 50% coverage. Although national coverage levels can "mask" sub-national geographical or sociological pockets where coverage is much lower, in 2006, 57% of children lived in countries with greater than 80% DTP3 coverage. Still, that year approximately 26.3 million children who reached their first birthday did not receive DTP3, but 16.2 million (62%) of them lived in China, India, Indonesia or Nigeria. At the time this report was prepared, there remained seven countries where fewer than half of the children were vaccinated with three doses of DTP3: Angola, Central African Republic, Chad, Equatorial Guinea, Gabon, Niger and Somalia."
WHO and UNICEF publish annual estimates of national immunization coverage; (27-30) such estimates have been available by country since 1980 at http://www.who.int/immunization_monitoring/en/globalsummary/ wucoveragecountrylist.cfm and http://www.childinfo.org/immunization_countryreports.html. Additional analyses can be found at http://www.who.int/immunization_monitoring/data/en/and http://www.childinfo.org/Immunization.htm. This paper describes the data, methods, assumptions and processes used to develop these estimates.
Key data sources
Administrative data based on reports from service providers (e.g. health centre staff, vaccination teams, private physicians) and surveys with items on children's vaccination history are the main sources of empirical data on immunization coverage. Administrative data report the number of vaccinations administered during a given period--usually 1 month--to local public health authorities who review the data and take any necessary action. The data are then aggregated and reported to the next administrative level and later aggregated, analysed and used at the national level to determine immunization policy, focus programme activities and influence resource allocation. National coverage data are reported...
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