Wealth Divide Leaves Nigeria’s Poorest Children Most Vulnerable to Missed Vaccines

Childhood vaccination is one of the most cost-effective interventions in public health, yet its benefits are not distributed evenly across societies. A new study from Nigeria, published in the International Journal for Equity in Health, provides some of the most detailed evidence yet on how a family’s wealth shapes both a child’s risk of being under-immunized and the ease with which caregivers can reach vaccination services. Drawing on household survey data from six states spanning all six of Nigeria’s geopolitical zones, the research team led by Ifunanya Clara Agu of the University of Nigeria found a consistent pattern: the richer a household, the easier it is to access vaccination, and the poorer a household, the more likely its children are to miss out on recommended immunizations.

The study surveyed 1,734 caregivers of children under five years of age, using a questionnaire adapted from the World Health Organization’s Behavioural and Social Drivers, or BeSD, tool. This instrument is designed to capture not just whether a child is vaccinated, but the psychological and practical factors that drive vaccination behavior, including perceptions of service quality, social norms, and ease of access. The researchers selected one state from each of Nigeria’s six geopolitical zones, giving the survey a geographic breadth that reflects the country’s considerable diversity in culture, health infrastructure, and economic conditions.

A central methodological feature of the study was its measurement of socioeconomic status. Rather than relying on self-reported income, which is often unreliable in settings where much economic activity is informal, the team constructed a wealth index from household assets and living conditions using principal component analysis. Households were then ranked and divided into five socioeconomic quintiles, from the poorest twenty percent to the richest twenty percent. This approach, widely used in health equity research, allows researchers to compare health outcomes across the full wealth spectrum of a population and to detect gradients that would otherwise remain hidden.

The headline findings reveal a stark wealth gradient in access. Among caregivers in the poorest wealth quintile, 56.8 percent reported that accessing vaccination services was very easy, with a 95 percent confidence interval of 51.5 to 62.0 percent. In the richest quintile, that figure rose to 75.6 percent, with a confidence interval of 70.8 to 79.9 percent. In other words, caregivers in the wealthiest households were roughly twenty percentage points more likely to describe vaccination access as effortless than those at the bottom of the wealth distribution. The gap extended to affordability as well: 49.6 percent of the poorest caregivers said vaccination costs were very easy to afford, compared with 68 percent of the wealthiest, a difference that persists even though routine childhood vaccines themselves are typically provided free of charge through Nigeria’s immunization program.

Under-immunization followed the opposite gradient. Among all under-immunized children identified in the survey, 26.0 percent came from the poorest wealth quintile, compared with just 14.6 percent from the richest quintile. This means that children in the poorest fifth of households were substantially overrepresented among those missing vaccinations, a pattern that compounds existing disadvantage. Unvaccinated and under-vaccinated children face elevated risks of diseases such as measles, pertussis, and diphtheria, and clusters of under-immunized children can sustain transmission chains that threaten entire communities, including those with better overall coverage.

To move beyond simple descriptive comparisons, the researchers employed concentration indices, a standard tool in health economics for quantifying the degree to which a health outcome is distributed across the socioeconomic spectrum. For binary outcomes such as ease of access, they used the Erreygers-corrected concentration index, which corrects for the bounded nature of such variables and allows fair comparisons across studies. For ordinal variables, they used bounded concentration indices. The results were statistically unambiguous. Ease of access showed a concentration index of 0.035, significant at p less than 0.001, indicating a pro-rich distribution: the better the access, the more it was concentrated among wealthier households. Affordability showed a nearly identical index of 0.034, also highly significant. Under-immunization, by contrast, showed a negative concentration index of -0.048, with p equal to 0.005, confirming that the burden of incomplete vaccination was concentrated among the poor.

The directionality of these findings matters for policy. A pro-rich concentration index for access combined with a pro-poor concentration index for under-immunization describes a classic inequity trap: the children who most need the protective benefits of vaccination are precisely those whose families face the greatest barriers to obtaining it. Barriers for poorer households in Nigeria typically include longer travel distances to functional health facilities, unreliable service availability, out-of-pocket costs for transport and incidental fees, and opportunity costs of time lost from work or trading. Each of these weighs more heavily on a household with few resources, and the new study confirms that these burdens translate into measurable differences in immunization outcomes.

Nigeria’s immunization landscape provides important context for interpreting these results. The country operates an Expanded Programme on Immunization, administered through the National Primary Health Care Development Agency, delivering vaccines including the diphtheria-tetanus-pertussis-containing vaccine through primary health centers and periodic outreach campaigns. Despite decades of investment, national coverage has historically lagged behind targets, and progress has been uneven across regions and social groups. Previous studies have documented geographic disparities between northern and southern states and between rural and urban areas, but the new analysis adds a rigorous socioeconomic dimension, showing that even within the same zones, wealth itself is a powerful predictor of vaccination access and status.

The authors argue that reducing these inequities requires equity-focused immunization strategies that harness resources across all sectors, not just the health system. In practice, this could mean targeting the poorest quintiles with intensified outreach, removing informal costs at the point of service, compensating caregivers for transport, aligning vaccination sessions with market days to reduce opportunity costs, and systematically monitoring socioeconomic disparities so that adaptive strategies can be mobilized early. The study’s call for systematic monitoring is particularly significant: concentration indices can be recalculated with each new survey round, giving program managers a quantitative yardstick for whether equity is improving or deteriorating over time, and whether societal disruptions such as economic shocks or insecurity are reinforcing under-immunization among vulnerable groups.

The research was supported by the Alliance for Health Policy and Systems Research, with funding from the National Institute for Health and Care Research using UK international development funding, and it passed ethical review both at the University of Nigeria Teaching Hospital and in each of the six study states. Its message is ultimately one of both warning and opportunity. Nigeria will not close its immunization gap by improving average coverage alone; the averages conceal a persistent wealth divide that leaves the poorest children behind. By measuring inequity directly and embedding equity targets into immunization planning, health authorities can direct resources where they will save the most lives, ensuring that no child’s protection against vaccine-preventable disease depends on the size of their family’s wealth.

Subject of Research: Socioeconomic inequities in childhood vaccination access and under-immunization in Nigeria

Article Title: Pro-rich or pro-poor? socioeconomic inequities in under-immunization and access to childhood vaccination services in Nigeria

Article References: Agu, I. C., Ekwueme, C. N., Mbachu, C. O., Ezue, U. N., Obiobasi, I., & Onwujekwe, O. (2026). Pro-rich or pro-poor? socioeconomic inequities in under-immunization and access to childhood vaccination services in Nigeria. International Journal for Equity in Health. https://doi.org/10.1186/s12939-026-03046-z

Image Credits: AI Generated

DOI: 10.1186/s12939-026-03046-z

Keywords: childhood vaccination, Nigeria, socioeconomic status, health equity, under-immunization, concentration index, access to health services, wealth index, immunization policy, low- and middle-income countries, BeSD tool, primary health care