Improving Routine Childhood Immunisation Outcomes in Low-Income and Middle-Income Countries: An Evidence Gap Map

"[T]his map can serve as a tool for policy-makers and practitioners working in the routine immunisation space to find rigorous evidence to inform decisions about which programmes to implement and how to implement them..."

Even with adequate vaccine availability, national immunisation systems in many low- and middle-income countries (LMICs) are unable to achieve high immunisation coverage, which requires both reliable health service delivery and attenuation of behavioural, social, and practical constraints faced by caregivers. Thus, multipronged approaches that provide contextualised solutions to address constraints and barriers are needed. To help support evidence-informed decision-making in light of various approaches, this study presents an evidence gap map (EGM) of impact evaluations (IEs) and systematic reviews (SRs) measuring the effects of interventions on outcomes related to routine child immunisation in LMICs. An EGM aims to establish what is known and unknown about an evidence base in a thematic area. The analysis here is complemented by an interactive online map.

Drawing on the literature on routine child immunisation in LMICs, the researchers developed a theory of change featuring key factors - from the perspectives of caregivers and communities, vaccinators, health systems and beyond - that influence whether children receive the full course of routine vaccinations. These factors form the basis for an intervention-outcome matrix with 38 interventions and 43 outcomes.

The theory of change suggests how interventions may be oriented to address aforementioned key factors and lead to greater immunisation coverage and better health outcomes. It suggests that interventions directed at caregivers and communities create greater desire, motivation, awareness, opportunity, and decision-making power to pursue vaccination services (behavioural, social, and practical factors). Interventions aimed at health providers and systems increase their capacity and accountability to deliver quality and timely vaccination services. Interventions addressing non-health barriers such as poor road infrastructure facilitate better delivery of vaccination services. Addressing behavioural, social, and practical barriers faced by caregivers and communities, along with improved service delivery, increase the number of children who receive all vaccine doses on time. Full and timely immunisation coverage, in turn, reduces morbidity and mortality in the population.

The researchers searched academic databases and grey literature sources for relevant IEs and SRs. Studies meeting the eligibility criteria were included, and data were extracted for each included study. The researchers analysed these data to identify trends in the geographic distribution of evidence, the concentration of evidence across intervention and outcome categories, and attention to vulnerable populations in the literature.

This process led to the identification of 309 studies, comprising 226 completed IEs, 58 completed SRs, 24 ongoing IEs, and 1 ongoing SR. Evidence from IEs is heavily concentrated in a handful of countries in sub-Saharan Africa and South Asia. Many studies evaluated interventions that included multiple components (e.g., training for health workers (HWs) and sensitisation meetings with women). The researchers decided to capture all major intervention components for each study. That is, some studies have multiple intervention codes applied to them. In this way, the EGM can be considered a map of "instances of evidence" rather than a map of studies.

In general, interventions providing education, training, or incentives to either caregivers or HWs are among the most commonly evaluated. Although interventions providing knowledge and education to caregivers are frequently evaluated, only four IEs have explicit components aimed to dispel misinformation or misconception regarding vaccination, and only one SR touches on it. Among interventions leveraging community engagement, there is a concentration of evidence on the use of community dialogue for increasing immunisation coverage (26 IEs and 15 SRs). There is comparatively little work on non-material incentives for caregivers (3 IEs, 1 SR), which includes, for example, community recognition as an incentive to vaccinate. Among interventions to motivate HWs, pay-for-performance schemes are by far the most commonly evaluated (27 IEs, 14 SRs).

Several evidence gaps are evident. For example, there are significant gaps in outreach to migrant populations (one IE, no SRs) and campaigns to vaccinate refugee populations (no IEs or SRs). In addition, the researchers did not identify any IEs or SRs with interventions framed specifically as outreach to vaccine-hesitant groups, although there is some evidence on outreach to vulnerable populations (10 IEs, 8 SRs), which may overlap with vaccine-hesitant groups to some extent. There is a potential synthesis gap with respect to community HW training and education, for which there are 22 IEs but no medium-confidence or high-confidence SRs.

Among outcomes, those related to vaccine coverage and health are well covered. However, evidence on intermediate outcomes related to health system capacity or barriers faced by caregivers is much more limited. Regarding outcomes related to behavioural, social, and practical barriers faced by caregivers and communities, some outcome categories are relatively well studied, while others have very little evidence. For instance, the researchers identified 18 IEs and 8 SRs that considered caregivers' attitudes about immunisation; in contrast, few studies examine the social processes affecting caregivers' vaccination decisions (five IEs, one medium-confidence SR) or their readiness to vaccinate (four IEs, six SRs). Only two specific outcome categories on the caregiver side of the framework were examined in more than 10 studies: caregivers' knowledge about immunisation (16 IEs, 5 SRs) and retention of vaccination cards (12 IEs, 2 SRs).

The researchers conclude: "There is valuable evidence available to decision-makers for use in identifying and deploying effective strategies to increase routine immunisation in LMICs. However, additional research is needed to address gaps in the evidence base." To cite only one example, while the researchers identified a concentration of evidence on use of community dialogue for increasing immunisation coverage, the amount of evidence on use of community resources, such as local leaders or selected community groups, to promote vaccination is relatively small. "With community engagement approaches featuring prominently in the Global Vaccine Action Plan,... it will be important to further strengthen this evidence base for better guidance on programming and policy."