Understanding Household-Level Risk Factors for Zero Dose Immunization in 82 Low- and Middle-Income Countries

"...underscores important opportunities to strengthen the quality of maternal care and improve the integration of maternal, neonatal, and child health programs to mitigate missed opportunities for vaccination as an approach to reach zero dose children."

In 2021, an estimated 18 million children did not receive a single dose of routine vaccinations. Beyond identifying vulnerable contexts where zero-dose children live, it is important to understand the risk factors and barriers they face in accessing care. The objective of this paper is to quantitatively and qualitatively describe the profile of zero-dose children in low- and middle-income countries (LMICs) with the hope of helping child health and immunisation managers design and implement new approaches to engage vulnerable children in immunisation systems and, more broadly, in the health system.

The researchers developed a theoretical framework to describe the multi-level correlates of zero-dose status. The top level of the framework includes macro-level contextual factors related to community beliefs, political support, governance, gender norms, and location-related fragility. The contextual factors affect the next set of more proximal factors: household, health system, and individual psychosocial factors. Household factors are related to sociodemographic status, engagement with services and resources (e.g., health and education services, access to media or internet), family-level gender dynamics (e.g., decision-making autonomy), and the ease of reaching vaccination services. Household-level factors like decision-making autonomy and ease of accessing services are likely to affect individual psychosocial factors, and past experiences in health facilities affect the trust in health system and motivation to seek services. Household factors are the focus of this analysis.

The study is based on Demographic and Health Surveys (DHS) and Multiple Indicator Cluster Surveys (MICS) data spanning 2011 to 2020 from low, lower-middle, and upper-middle income countries. Zero-dose status was defined as children aged 12-23 months who had not received any doses of Bacille Calmette-Guérin, DTP-containing, polio, and measles-containing vaccines. The researchers estimated the prevalence of zero-dose children in the entire study sample, by country income level, and by region, and they characterised the zero-dose population by household-level factors. Multivariate logistic regressions were used to determine the household-level sociodemographic and health care access factors associated with zero-dose immunisation status. To pool multicountry data, the researchers adjusted the original survey weights according to the country's population of children 12-23 months of age. To contextualise our findings, the researchers used United Nations Population Division birth cohort data to estimate the study population as a proportion of the global and country income group populations.

Eighty-two countries were included in the univariate analyses and 68 countries in the multivariate model. Overall, 7.5% of the study population were zero-dose children. More than half (51.9%) of this population was concentrated in African countries. Zero-dose children were predominantly situated in rural areas (75.8%) and in households in the lowest 2 wealth quintiles (62.7%) and were born to mothers who completed fewer than 4 antenatal care (ANC) visits (66.5%) and had home births (58.5%). However, a considerable proportion of zero-dose children's mothers did receive appropriate care during pregnancy (33.5% of zero-dose children have mothers who received at least 4 ANC visits). When controlled for other factors, children had 3 times the odds (OR = 3.00, 95% confidence interval (CI): 2.72, 3.30) of being zero dose if their mother had not received any tetanus injections, 2.46 times the odds (95% CI: 2.21, 2.74) of being zero dose if their mother had not received any ANC visits, and had nearly twice the odds (OR = 1.87, 95% CI: 1.70, 2.05) of being zero dose if their mother had a home delivery, compared to children of mothers who received at least 2 tetanus injections, received at least 4 ANC visits, and had a facility delivery, respectively.

Other selected findings: 6.9% of children living in female-headed households are zero dose, which is slightly lower than the global average of 7.5%. Globally, children of mothers who did not receive education were 32% (95% CI: 20%, 46%) more likely to be zero dose than children of mothers who completed only primary education. Children of adolescent mothers (15 to 19 years), compared to children with mothers at least 20 years of age, are 31% (95% CI: 13%, 52%) more likely to be zero dose at the global level. The fact that limited maternal education and adolescent age affect zero-dose status highlights the need for gender-responsive approaches to reach zero-dose children and their families. Also, there is a higher proportion of zero-dose children among those whose mothers access TV and radio less than once a week (11.1% and 8.2%, respectively).

Although some zero-dose children remain entirely excluded from the health system, the findings reveal that a large proportion of zero-dose children and their families do have existing connections with the health system. For instance, a third of zero-dose children had mothers who received 4 or more ANC visits. One of the secondary objectives of ANC is to provide mothers with information, resources, and a pathway to protect themselves and their infants against vaccine-preventable diseases. Optimising this process or understanding its shortcomings could be critical to reaching zero-dose children.

The fact that 76.0% of children of mothers with 0 ANC visits and 80.6% of children of mothers without tetanus injections are not zero dose perhaps shows the strength of community outreach of vaccination programmes. Perhaps additional efforts to provide vaccination services in communities play an important role in reaching families who do not interact with the fixed health facility.

Per the researchers, future work should focus on identifying best practices and approaches to identify and reach unimmunised children. Zero-dose children experience unique barriers that can exclude them from the health system entirely; it is therefore necessary to identify, develop, and scale interventions, such as improved community-based microplanning, that can respond to these barriers and engage them with the immunisation system for the first time. This study also underscores the association between access to maternal health services and immunisation uptake and makes an argument for stronger collaboration between maternal and newborn health and immunisation managers.