Inequalities in full immunization coverage: trends in low- and middle-income countries

Despite the improvements made in global immunization coverage for children over the past decade,1,2 an estimated 21.8 million infants worldwide are still not being reached by routine immunization services.3 In 2013, most of the World Health Organization’s (WHO) regions reached more than 80% of their target populations with three doses of diphtheria, pertussis and tetanus (DTP) vaccine but coverage with such vaccine remained well short of the 2015 goal of 90%, particularly in the African (75%) and South-East Asia regions (77%).2,3 Many barriers exist to achieving good vaccination coverage, including a lack of parental education, low income, poor access to health facilities and traditional beliefs.4–13 As progress in this field is commonly expressed in terms of national or regional mean values, many of the underlying disparities among and within countries go unobserved or, at least, unreported. If routine immunization is to be made fast and equitable, we need multi-country studies that use the same types of stratification to document and understand the inequalities in vaccination coverage at both national and regional level.1,3,14,15 We also need to know the percentages of children who receive the full set of standard vaccines recommended by WHO. In India, for example, national immunization coverage has been increasing since the early 1990s but the proportion of children who, in 2006, had received all of the immunizations recommended for their age group as part of WHO’s Expanded Programme on Immunization was still under 50%.16 Failures or delays in the vaccination of children in high-risk groups can limit the impact of vaccine programmes on the burden of disease.17

The main objectives of the present analyses were: (i) to assess the proportions of children in low- or middle-income countries who receive a basic set of routine vaccinations – that is one dose of bacille Calmette-Guérin vaccine, one dose of measles vaccine, three doses of vaccine against DTP and three doses of polio vaccine – at the appropriate ages; (ii) to document between-country and within-country inequalities in such coverage – in terms of socioeconomic status and other characteristics commonly recorded in national surveys; and (iii) to assess temporal trends in such coverage and in the associated inequalities.