Introduction
Systematic research exploring the impacts of mass vaccination campaigns on health systems began in the 1990s, with a study led by Carl Taylor examining the impact of polio campaigns on health systems in the Americas.1 This report concluded that the polio programme had largely positive though varying effects on health systems, yet warned readers against extrapolating the findings to other regions. This work established two modes of thought that shaped future research in profound ways. First, it evaluated the impacts of vertical programmes on health systems separately from the question of whether they achieved their own internal goals. The Taylor Commission did not evaluate the efficacy of the polio programme itself; the programme had already succeeded at eliminating polio in the region.
Second, the report evaluated the impacts of vertical programmes on health systems in a binary manner, with impacts separated by health system component, and categorised as positive or negative. For example, the polio programme had a significant positive effect on management strategies of the broader health system; it had a modest positive effect on interagency and intersectoral collaboration; and a significant negative effect on availability of scarce resources—‘vaccination campaigns were resented because everything else had to be interrupted in order to carry them out’ (p61). The Taylor Commission was fully aware that these impacts were complex—in some categories, both positive and negative effects were listed—but the framework for presenting these effects was relatively simple.
In the intervening 25 years, there has been a great deal of sophisticated research evaluating the impacts of mass campaigns on health systems within a variety of settings.2–10 This body of work has described the push and pull between campaign-based and routine delivery strategies,10 and highlighted the inherent tensions in trying to leverage eradication initiatives for health systems strengthening.11 This research has largely hewed to the methodological precedents of separating the impacts of campaigns by health system component, and considering impacts in a binary manner.12 These methodologies were adopted because they provided a straightforward way of examining complex systems.
Yet the simplicity of the dominant frameworks limited their utility, as the researchers involved were well aware. In 2014, the authors of three studies on mass vaccination campaigns argued that better frameworks for such studies were needed. ‘Health systems are complex,’ they wrote, ‘like a living organism, they are dynamic, with interacting components—at various geographical levels—that lead to adaptation and to the emergence of new dynamics’.12 Subsystems such as routine immunisation (RI) are also complex and dynamic.13
While systems thinking approaches have been increasingly applied to complex phenomena in global health,14 15 they remain underutilised. With the advent of global COVID-19 vaccination campaigns, there is renewed attention both on how to maximise an individual campaign’s effectiveness16 as well as plan a campaign to benefit the health system.17 18 This work continues to consider the health systems impacts of campaigns separately from the success of the campaign itself.
To move beyond these prevailing ways of thinking requires describing health systems as they are—complex, dynamic and tightly linked—and making explicit the relationships between elements of the system which affect system outputs and outcomes over time. We propose a complex adaptative systems (CAS) lens. CAS thinking includes the notion of ‘path dependency,’ that processes with similar inputs and governing mechanisms may lead to very different outcomes,19 and emphasises the unintended, even paradoxical, effects that can occur within these complex systems.19 20
We use CAS to explore the relationships between polio campaigns and health systems in Ethiopia, India and Nigeria. Unlike previous analyses, which have focused on the polio programme’s impacts on health systems, our analysis focuses on how interactions between the polio programme and the health system influence two key outcomes, frontline health worker (FLHW) motivation and vaccine hesitancy. (We take the definition of vaccine hesitancy as ‘delay in acceptance or refusal of vaccination despite availability of vaccination services’21; hesitancy has multifactorial determinants, including issues beyond the vaccine itself, and varies by population and context22–24). These two factors, in turn, affect campaign coverage in the polio programme itself.