While the global immunization coverage, estimated as the proportion of world’s children who received all doses of the basic vaccines (BCG, polio, DPT, and measles), has remained stable at 85% since 2010, there were about 13.5 million children under one year of age who did not receive those vaccines in 2018.

We explored the magnitude of inequality in the immunization cascade in children aged 12-23 months according to the family’s socioeconomic position, the child’s sex, and place of residence in 92 countries. The immunization cascade was calculated as a score with five levels, representing children who did not receive any doses of either of the basic vaccines (named zero-dose children), and children who received at least one dose of 1, 2, 3, or all four types of vaccines.

Of all children studied, 8% were in the zero-dose group, 3% each in the second and third step, 15% in the fourth, and 71% in the fifth step with four vaccines. This J-shaped pattern reflects a degree of polarization among children who have little or no access to immunizations, and those who receive most if not all vaccines.

We found sharp inequalities according to household wealth, with zero-dose prevalence ranging from 13% in the poorest to 3% in the wealthiest quintile across all countries. The J-shaped pattern was particularly evident among children from poor families in low- and lower-middle-income country groups, but it was not observed in upper-middle income countries, where the proportion of zero-dose children was low in both the poorest and wealthiest quintile.

Our analysis highlights that reaching zero-dose children and addressing barriers to under-immunization will likely improve equity in immunization coverage.

Full text link: https://www.sciencedirect.com/science/article/pii/S0264410X21002632