Figure 1 presents the full CLD depicting the role of trust and communication in the utilization of health services and vaccines. The top part of the diagram illustrates the determinants of utilization including vaccine readiness (e.g. availability of vaccines, functional cold chain, vaccinators) and health systems readiness (overall capacity of health systems to provide general health services). In the center of the diagram is utilization of vaccines and the health system, which directly reduces the avertable disease burden. We propose that the health system and immunization system utilization are directly influenced by trust and the respective pathways of influence are illustrated in the central core of the diagram. Trust in the health system is shaped by positive and negative messages about the health system. Similarly, trust in vaccination is influenced by the messages about vaccines that can arise from both within and outside the community.
The multitude of loops illustrate the tight direct and indirect connections between the health system and the immunization system, as well as the pathways through which trust is built. We propose that health system utilization can reinforce vaccine utilization directly (see Fig. 1, R1). Similarly, the greater the trust in the health system, the greater the trust in vaccination (Fig. 1, R3). The relationship between health system utilization and trust is uncertain (Fig. 1, U4). While we posit that increased trust would certainly lead to greater utilization of services or vaccines, how the utilization experience affects trust is context-dependent. If the health system provides users with a positive experience and outcomes, then the trust in the health system would increase. However, if the experience from utilization is not positive, then increasing health system or vaccine utilization could lead to decreased levels of trust in the health system and vaccination, respectively (Fig. 1, U4 and U2). In order to build trust, the CLD shows that it is essential for utilization of health systems and vaccines to lead to positive experiences that generate positive messages following the experience of the user.
We identified further uncertainty in the relationship between health system utilization and both positive and negative messages. Ideally, increased community health system utilization would lead to increasing positive messages and decreasing negative messages. However, when the quality of health services is compromised, those utilizing services would actually contribute to propagating negative messages, rather than positive ones (Fig. 1, U5). Similarly, increased utilization of the health system causes increased trust in the health system, only in situations when the experience and outcomes are favorable (Fig. 1, U6). Following the same logic, a similar uncertainty is seen in the immunization system (Fig. 1, U10 and U13). We explore these uncertainties further through the scenarios below.
Scenario 1: poor health systems readiness as a result of a shock to the health system
Weak health systems represent a root challenge to most, if not all health interventions in LMICs, including routine immunization. Critical events, such as the Ebola crisis or political conflict whose shocks ripple through the health system and ultimately affect service delivery, can exacerbate weaknesses of a health system. In Fig. 2, we illustrate how health system shocks not only influence trust in the health system, but that these issues eventually spillover into the immunization system as well, likely with a delay. In response to decreasing system readiness, a reinforcing vicious cycle develops between health care utilization and trust (Fig. 2, R4). As distrust in the health system builds, this in turn generates negative messages about the health system which again impacts utilization [20]. The CLD illustrates that all of these interactions reinforce the linkage between poor health systems readiness and low health systems utilization. Loops R5 and B6 further reinforce decreases in trust in the health system, which reinforces the decrease in trust in vaccination (Fig. 2, R3).
It is important to note the trickle down effects that the health system has on vaccination. Poor health system readiness can affect vaccine readiness, influencing utilization of vaccines. In the central part of Fig. 2, we observe that under-utilization of the health system reinforces under-utilization of vaccines and vice versa (Fig. 2, R1). Low utilization of vaccines increases distrust in vaccination (Fig. 2, R2), and distrust in vaccination reinforces distrust in the health system (Fig. 2, R3). Greater distrust in the health system reduces utilization of the health system (Fig. 2, R4), completing the reinforcing loop that links utilization with distrust, and health systems with vaccines.
While it is commonly understood that poor vaccine readiness would trigger under-utilization and distrust in vaccination, we show that distrust in vaccination can also be triggered by poor health system readiness. Even if the vaccine were available, the perceived weakness of a health system, especially following a shock, can have an effect on distrust and utilization. Even after a health system recovers from disruption, distrust tends to remain, resulting in a delay in recovery for utilization. For example, this link was observed in Sierra Leone when the Ebola virus stressed the fragile health system and degraded essential healthcare provision, resulting in a more than 20 % decrease in childhood immunization in health facilities [21]. The decrease was attributed both by lack of services from closed facilities or shortage of supplies, but also to lack of trust in the health system – i.e. community fear of going to health facilities.
Restoring health system readiness is one of the remedies to rebuilding trust. However, that alone might not be sufficient. Community-level communication and messaging – perhaps tapped through community engagement is another key pathway. Demonstrating health system responsiveness through organizing immunization campaigns, which ensure that immunizations reach children outside of the facility provides another option. This can create a temporary parallel pathway, but can help to maintain trust in vaccination, and therefore positively reinforce trust in the health system while general re-building efforts are underway.
Scenario 2: anti-vaccine messages
Anti-vaccine messages, myths, and negative media fuels distrust in vaccination. Negative messages about vaccines may come from beyond the community, through the media, interest groups and others in forms of rumors and stories [16]. Such messages may include suspected adverse events following immunization, conspiracies of the government and the pharmaceutical industry, fear instilled by the debunked study linking vaccines with autism, or discussions of parental rights alongside religious or naturalist beliefs. These messages are especially persistent in contexts where disease prevalence has gone down and where parents question vaccinating healthy children against something that they no longer perceive to be a relevant concern [16]. These negative messages build distrust in vaccination (Fig. 3, R7), develop vaccine myths within the community (Fig. 3, R8) and reinforce vaccination distrust (Fig. 3, R9). For example, the 2012 WHO-UNICEF Joint Reporting Form found that 19 % of un- and under-vaccinated individuals in Uganda cited lack of confidence as a factor that influenced their vaccination decision [22]. This demonstrates that lack of confidence or trust can be a significant problem even in low-income settings. Vaccine myths reduce utilization of vaccines, which further increases distrust (Fig. 3, R10). Low utilization of vaccines may continue to reinforce myths within communities (Fig. 3, R11).
There are also spillover effects from vaccines onto the health system. Distrust in vaccination can feed into distrust in the health system, leading to under-utilization of the health system. Distrust in vaccination may be triggered by poor vaccine readiness in addition to anti-vaccine messages. Therefore, improving vaccine readiness may not be sufficient to gain people’s trust and increase utilization of vaccines.
The CLD suggests two possible critical junctures to reverse or mitigate the effects of anti-vaccine messages. First, the negative messages could, in certain instances, be countered by increasing positive messages about vaccines. A recent review of the published literature suggests that dialogue-based interventions can be effective in addressing vaccine hesitancy [23]. Moreover, individually and culturally tailoring messages about vaccines is important, in order to respond to the varied types of views parents can hold [24, 25]. However, positive messages on their own will likely not counteract negative messages. Often anti-vaccine messages are more enticing than positive ones as diseases that are prevented do not make news. In addition, ‘negativity bias’ may result in anti-vaccine information having much more influence than pro-vaccine information, making it easier to lose people’s trust than it is to gain it [26]. Furthermore, recent studies suggest that positive vaccine messages or information about the risks of the disease may not always have the desired effect, reinforcing anti-vaccine sentiments among those who are already hesitant to vaccinate [27, 28]. These studies have mostly been conducted in high-income country contexts, leaving room for further exploration in low- and middle-income country settings [29, 30]. While spreading positive messages is unlikely to be a sufficient solution, it may be essential to integrate it as part of a broader package of multi-component interventions to counter reduced utilization triggered by anti-vaccine messages.
The second and equally important option is to increase the numbers of those who have positive experiences with vaccines, so that vaccine myths decreases and distrust reduces. By building positive experiences with utilization, positive messages and trust are more likely to develop than myths and distrust.
Scenario 3: strong social capital
Where there is strong social capital, or high collective value of social networks of community members, and utilization of vaccines and the health system generates positive experiences, positive messages about vaccines within a community can be cultivated. Strength of social capital is assessed by the collective value of social networks (i.e. who people know) and the type of interactions that arise (e.g. norms of reciprocity) [31]. When communities collectively spread positive messages about vaccines, this builds trust in vaccination (Fig. 4, R12) and increases utilization of vaccines, which can yet again foster positive messages (Fig. 4, R13). This may explain how higher social capital is associated with higher immunization coverage [32]. We also recognize that the opposite might be true in certain cases. High social capital, in communities that have a poor experience with the health system or immunization system, as well as resistance to public health evidence, could lead to negative messages that are cultivated and sustained [33].
Strong positive social capital is essential for public health measures such as vaccination whereby members of the community would provide benefits to others. Vaccination protects the vulnerable in the community who cannot be immunized through indirect protection known as herd immunity, further reducing avertable disease burden [10]. Social capital in the context of positive messages about vaccines within the community can influence trust in and utilization of vaccines, which can impact trust in the health system leading to increased health system utilization (Fig. 4, R14) as well as spread positive messages about the health system (Fig. 4, R15) and affect the health of the population [34].
Social capital is important for community resilience – the greater the social capital in a context in which services are satisfactory, the less a community would be impacted by negative messages. With social capital, communities would also have a common voice to raise concerns to ensure accountability of healthcare services. The positive feedback loops (Fig. 4, R12-R15) build on community solidarity and are essential in building system resilience.
Strong social capital in a community can also spillover to neighboring communities. Positive messages about vaccines may travel beyond the immediate community to others, increasing messages beyond the community and building trust in new communities Fig. 4, R16). Such messages can unlock community capabilities to increase healthcare utilization and reduce preventable diseases. For example, strong positive social capital observed in Niger suggested that a community-based approach could improve the level of comprehensiveness and sensitivity of disease surveillance [35]. In Ethiopia, “low social capital and low economic status were associated with higher under-five mortality compared with those better-off” and those with high social capital were found to be more likely to be vaccinated [36].