Strengthening Vaccination Delivery System Resilience in the Context of Protracted Humanitarian Crisis: A Realist-informed Systematic Review

"...no 'silver bullet' solution exists to promoting resilience in vaccination delivery systems in protracted humanitarian crises..."

Childhood vaccination coverage in many humanitarian settings is sub-optimal. This systematic review examines evidence on the effectiveness of system-level interventions for improving vaccination coverage in protracted crises, focusing on how they work, and for whom, to inform preparedness and response for future crises.

This was a realist-informed systematic review of peer-reviewed and grey literature published between January 1 2001 and September 11 2021, in Arabic, English, and French. The review was performed September 3-9 2021 in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The 50 included studies share evidence relating to vaccination delivery for refugee, internally displaced, and host community populations in low- and middle-income countries (LMICs) affected by protracted humanitarian crises (contexts in which United Nations (UN)-led humanitarian response plans had been in place for at least 5 years). The focus of the review is on children aged 0-5 but incorporates older displaced children, teenagers, and adults in consideration of, for example, catch-up programmes.

Included studies addressed interventions implemented in a range of settings, but the largest number of studies were from Nigeria (n = 15, 30%), followed by South Sudan and Afghanistan (n = 4, 8%), and Cameroon, Haiti, and Somalia (n = 3, 6%). Four studies (8%) addressed interventions applied across multiple settings. Most studies addressed either interventions targeting multiple antigens from the routine schedule (n = 17, 34%) or those aimed at improving coverage of different classes of poliomyelitis immunisation (n = 19, 39%). A smaller number considered cholera or measles vaccination specifically.

Table 2 in the paper provides a summary of the principal intervention types identified in the review, the mechanisms by which these were seen to act (categorised as either adaptive, transformative, or potentially transformative), a summary of relevant outcomes, and key contextual modifiers, including: the level of insecurity in the operating environment; the level of population trust in providers; and the existence of preexisting health system infrastructure (especially linked to polio eradication activities in security-compromised areas) around which to implement new interventions. A study-by-study summary of results is given in Additional file 4: Appendix 4. Highlights include:

Supply-side interventions

• Vaccination campaigns: Common strategies emerging across a number of the studies include the use of multiple service delivery pathways, intensive community engagement and mobilisation activities, and central coordination led by the domestic Ministry of Health, which in combination were intended to increase vaccination coverage by mechanisms including bringing services closer to users, enhancing awareness of the need for vaccination, and fostering trust in service providers.
• Health financing: Interventions ranged in focus from adaptive capacity building to potentially transformative activities. For instance, two studies considered improvements to local-level incentives for vaccination delivery (e.g., to improve health worker satisfaction and motivation to deliver vaccination). The overall picture from these studies was mixed.
• Service integration:
  • Two studies on the use of mobile health teams both showed statistically significant improvements in vaccination coverage, although the nature of these effects varied. The mechanisms by which mobile health teams worked had much in common across contexts, including the following: an element of population prioritising (especially in Nigeria, where mobile health teams for polio vaccination were deliberately directed to settlements in the North of the country that were deemed high-risk for further acute flacid paralysis (AFP) cases); intensive community engagement and outreach activities (integrated into the intervention through the inclusion of community mobilisers into the mobile health team in Nigeria, but parallel to it in Afghanistan) to promote awareness of, and trust in, services provided; a system of regular visits over time to build local population trust, rather than one-off interactions; and transparency regarding visit scheduling so that service users knew when teams would be in their locality.
  • Two low-quality observational studies considered the effect of integrating nutrition and immunisation services through single access points in South Sudan. The community focus of these integration efforts was important.
  • Two studies addressed integration of routine immunisation (RI) and polio services. One of these, a high-quality cluster randomised trial in security-compromised areas of Pakistan, showed statistically significant improvements in the proportion of fully vaccinated children (7.3% [95% confidence interval (CI) 4.5-10.0] increase in one arm vs control and a 9.5% [6.9-12.0] increase in the second arm vs control. In both the intervention arms, the key mechanism changes were (i) the provision of multiple service delivery pathways (collaterals) and (ii) the use of intensive community mobilisation activities that were delivered in a culturally sensitive way. The second study, a programme evaluation from Nigeria considering the integration of RI with polio eradication work, also emphasised culturally appropriate community outreach, through female community volunteer mobilisers, and saw a rise in the proportion of fully immunised children in the catchment areas from 18-49%.
• Governance and coordination: Three studies considered governance and coordination activities, two emphasising adaptive capacity through civil-military engagement and one describing transformative capacity change through intergovernmental cooperation. The key hallmark of the interventions in the first two was a "feet-on-the-ground" approach to improving uptake, including in areas of significant insecurity, and the use of "hit-and-run" approaches to vaccine delivery with security cover during periods of unrest.
• Workforce development, flexibility, and surge capacity: For example, one study looked at volunteer community mobilisers in Nigeria to address persistently low uptake in security-compromised areas, vaccine scepticism, and distrust in government and officials. In this study, volunteer community mobilisers had an integrative role that included supporting RI but also water, sanitation, and hygiene (WASH) and other interventions. This intervention showed evidence of improvements in coverage and a sharp decline in missed opportunities for vaccination (MOVs) - from 4.5% in 2014 to 0.8% in 2018 - which the study attributes to high levels of trust in volunteer community mobilisers because of their social position, cultural sensitivity of their approach, engagement modes including house-to-house visits, and their ability to update programme coordinators with information on pockets of low uptake.
• Health information and surveillance: For example, in one study, geographical information system (GIS) mapping was used to geo-locate population centres to inform the positioning of fixed sites for the campaign. This approach resulted in a reduction in the number of wards with zero vaccination coverage by comparison with states where standard population estimation approaches were used.

Demand-side interventions: Although the majority of studies referenced community engagement as a trust-building measure, four studies explicitly focusing on this aspect met the inclusion criteria for the review. They all involved multi-dimensional community mobilisation activities; one combined community mobilisation activities with direct observation of polio vaccination by officials to ensure proper administration of vaccination. All four were implemented in Nigeria, and most were concerned with improving polio vaccination uptake. These complex interventions involved multiple outreach strategies including the use of roadshows, in-kind incentives (e.g., provision of soap), health camps, communication via multiple channels, and agreement of mutually convenient vaccination point locations with community leaders; a number also incorporated recruitment and training of volunteer community mobilisers. Two of the four studies found declines in the proportion of children who had not received any oral polio vaccine (OPV) doses during the study period; another showed concurrent, large increases in pentavalent vaccination coverage.

Cross-cutting and multi-component interventions: Eight studies addressed sustained, multi-dimensional interventions. These interventions also tended to act at multiple levels. All emphasised the importance of strengthened coordination between key actors. For instance, a study from Somalia documented the introduction of a national polio control and coordination room to bring together key partners, improve communication, and provide a framework for information/intelligence sharing. Multi-modal social mobilisation activities were also central to achievement of improved outcomes.

Overall, some common mechanisms emerged across the higher-impact interventions identified in the review. For example, strengthening trust and increasing the range of access points were key themes, especially among communities living in security-compromised zones. Many interventions directly addressed these matters through outreach models including the use of community volunteers, messaging through community (including religious) leaders, and (more controversially) cooperation with security personnel. Community volunteers were frequently identified as critical in tackling scepticism towards government and officials; they also contributed to bolstering situational awareness through improved case ascertainment for vaccine-preventable diseases (VPDs).

Evidence in some areas was notable by its scarcity. For example, material on governance and financing was both limited and showed conflicting evidence on vaccination-related outcomes.

In short, creation of collaterals (multiple service delivery pathways) through service integration showed generally positive evidence of impact on routine vaccination uptake by bringing services closer to priority populations and leveraging trust that had already been built with communities. Robust community engagement emerged as a key unifying mechanism for outcome improvement across almost all of the intervention classes in building awareness and trust among crisis-affected populations. Some potentially transformative mechanisms for strengthening resilience in vaccination delivery were identified, but evidence for these remains limited.

Among the policy implications of the review: Periodic intensification of vaccination delivery via campaigns and supplementary immunisation activities (SIAs) is likely to be a mainstay of adaptive responses to crises whatever the context to account for shortfalls in routine delivery. However, the evidence included here suggests that recruitment of non-traditional workforce cadres from within affected communities - including community mobilisers - can help enhance uptake over the long-term, especially in security-compromised areas where trust in government and agency representatives may be low. Resilience in vaccination coverage is also likely to be enhanced through the concurrent use of multiple service channels to reach affected populations, including mobile health teams and integration with in-demand services such as nutritional support.

In conclusion: "Strengthening the resilience of vaccination delivery systems in protracted humanitarian crises depends on system adaptation across a range of areas, including bolstering access through strengthened outreach, multiple service pathways and better integration with other essential services, as well as demand-generation activities. Future work should consider evidence not just on adaptive and transformative measures to support improvements in vaccination coverage in these settings, but also economic analyses..."