Positioning implementation science in national immunization programmes to improve coverage equity and advance progress toward Immunization Agenda 2030: An urgent global health imperative

ABSTRACT

Despite the availability of effective vaccines for preventing common childhood infectious diseases, there is still significant disparities in access and utilization across many low- and middle-income countries (LMIC). The factors that drive these disparities are often multilevel, originating from individuals, health facilities, health systems and communities, and also multifaceted. Implementation science has emerged as a field to help address “know-do” gaps in health systems, and can play a significant role in strengthening immunization systems to understand and solve implementation barriers that limit access and uptake within their contexts. This article presents a reflexive perspective on how to position implementation research in immunization programmes to improve coverage equity. Furthermore, key points of synergy between implementation research and vaccination are highlighted, and some potential practice changes that can be applied within specific contexts were proposed. Using a human rights lens, it was concluded that the cost that is associated with implementation failure in immunization programmes is significant and unjust, and future directions for implementation research to optimize its application in practice settings have been recommended.

KEYWORDS:

• Implementation science
• immunization
• systems thinking
• complexity
• global health

Introduction

The critical role that vaccines play in inducing immunity against infectious agents makes them the backbone of communicable diseases prevention and control in human population.¹ In addition to protecting an immunized person, it has the advantage of indirectly protecting unvaccinated people (if coverage is optimal in that community).² This positive externality is significant for public health, and this is why vaccines are a key element of the global health security agenda.^2,3 Since the launch of the Expanded Programme on Immunization (EPI) by the World Health Organization (WHO) 50 years ago, there has been a remarkable global effort to ensure that all children are vaccinated for common infectious diseases that affect children like polio, measles, tetanus, and diphtheria among others.⁴ With the advent of global initiatives like Gavi, the Vaccine Alliance,⁵ low-and-middle-income countries (LMIC) have witnessed a dramatic increase in new vaccines that have been introduced to tackle organisms like Haemophilus influenzae type b, Streptococcus pneumoniae, and rotavirus which are commonly implicated in deadly diseases like pneumonia, meningitis, sepsis, and diarrhea.⁶ Countries have updated their immunization policies to integrate these new vaccines into their national schedules.

Inequity in vaccination coverage

Despite the availability of nationally recommended vaccines within health systems, multiple factors persistently hinders their optimal uptake across communities.⁷ This precipitates inequity in vaccination coverage level, which is a poor reflection of the performance of national immunization programmes.⁸ Inequity in vaccination coverage refers to variations in access and uptake of nationally recommended vaccines across communities due to contextual factors, which leads to the distortion of coverage level. This problem is more significant in sub-Saharan African countries.⁸ In the WHO African region, coverage with three doses of vaccines containing diphtheria, tetanus and pertussis (DTP3) was 72% in 2022 compared to the global coverage of 84%.⁹ DTP3 coverage has been stagnated at this level in the African region since 2021.⁹ Similarly, coverage of first and second dose of measles containing vaccines in 2022 are 69% and 45%, respectively, which are below the global estimates.¹⁰ However, coverage level vary between countries, for instance, 13 countries in the region which include Burkina Faso, Burundi, Carbo Verde, Eritrea, Eswatini, Ghana, Kenya, Mauritius, Rwanda, Sao Tome and Principe, Seychelles, Sierra Leone, and Zimbabwe achieved DTP3 coverage of 90% and above in 2022.⁹ Several studies have reported that vaccination coverage also varies within countries.^11–13 The problem with vaccination coverage inequity is that it deters progress toward achieving herd immunity at district and national level, and so child mortality from vaccine-preventable diseases (VPD) continue to occur.^14,15 In addition, there is frequent occurrence of outbreaks of VPD in the African region,¹⁶ and progress toward elimination goals for diseases like measles is being derailed.¹⁷ It is important to bear in mind that if vaccination coverage is not optimal across all communities, then, the health security risk posed by VPD will persist.

A vision for immunization for the decade (2021–2030)

At the beginning of this decade, the World Health Assembly (WHA) endorsed an ambitious immunization plan for 2021–2030.¹⁸ This is called the Immunization Agenda 2030 (IA2030) and it has set out several targets for immunization systems in the world to achieve by 2030.¹⁹ Some of the impact goal indicators in this agenda include attaining a 50% reduction in zero dose children; 90% global coverage for DTP3, three doses of pneumococcal conjugate vaccine (PCV3), two doses of measles containing vaccine (MCV2), and human papillomavirus vaccine (HPV); and aversion of 50 million future deaths globally from vaccination delivered by 2030 among others.¹⁸ To achieve these targets, there has been a progressive increase in global investment to make more vaccines available,²⁰ and efforts are currently underway to introduce new vaccines like the multivalent meningococcal conjugate vaccine and malaria vaccines to multiple countries where disease burden is high.²¹

Role of implementation research in immunization systems

Vaccines will not yield their desired public health impact if they remain in ice-lined refrigerators in central stores or health facilities. For this reason, the IA2030 emphasizes a higher momentum for implementation effectiveness so that these new (and even existing) vaccines actually reach the intended targets. This is reflected in the third and seventh strategic priorities of its framework for action which explicitly specified implementation research as a key area of focus. The goal of strategic priority 3 is to ensure that “everyone is protected by full immunization regardless of location, age, socioeconomic status or gender-related barriers” and strategic priority 7 is to ensure “innovations to increase the reach and impact of immunization programmes are made available to all countries and communities.”¹⁸

Implementation research emerged as a field of study to help address know-do gaps in health care settings.²² Several definitions of implementation research exist, but the most widely used is, “the scientific study of methods to promote the systematic uptake of research findings and other evidence-based practices into routine practice, and, hence, to improve quality and effectiveness of health services. It includes the study of influences on health care professionals and organizational behavior.”²² Implementation research is gaining prominence in global health because it seeks to strengthen health service delivery in routine settings and inform policymaking using real-world evidence to ensure sustainability.²³ There are evidence of health programmes that have used implementation research to enhance uptake of medicines and other innovations.²⁴

Coupling implementation research with national immunization programmes especially in the WHO African region where coverage gaps are most apparent can stimulate local testing of practical implementation strategies to address barriers in specific contexts.²⁵ This can potentially minimize variation in vaccination coverage across communities and districts. An implementation science lens can help programme managers of national immunization programmes and others stakeholders to conceptualize the factors that affect vaccination coverage as implementation determinants.²⁵ From a complex system perspective, the immunization programme is a complex adaptive systems, and so its valid to assume that implementation determinants constantly interact in a dynamic way across different communities and their relationships are characterized by emergent behavior, self-organization, and adaptability among others.²⁶ Understanding this non-linear causal relationship between implementation determinants exposes leverage points for interventions (such as context-relevant and locally feasible implementation strategies) to improve programme performance.²⁷ Reflexively, vaccine implementation research can be conceptualized as the application of implementation science frameworks, methods and approaches in complex healthcare settings to understand and control the influence of contextual factors that affect vaccination efforts to improve programme performance.

As shown in Figure 1, the rift between vaccines (new and existing) and their optimal use in routine practice settings across various communities can be progressively narrowed using implementation research.

Figure 1. Implementation research in immunization programmes.

Leveraging implementation science to improve immunization systems performance

Within the context of routine vaccination, the availability of vaccines and having fully immunized children represent two ends of a spectrum, and in between is implementation i.e. the active process involved in getting the vaccines to the target children to immunize them. In the organizational systems of routine vaccination, multiple system components such as people (caregivers and health workers), health facilities, primary health care structures (including institutions), policies, politics, society and government are involved in moving nationally recommended vaccines along this spectrum, and each one has its inherent characteristics which can differ from place to place.²⁶ Even though these components are interconnected and interrelated, the behavior of each one can be unpredictable; favorably or unfavorably influencing vaccination efforts.²⁶ It is this complex interaction between immunization system components that is responsible for producing the disparities that is observed in vaccination coverage levels.

Therefore, immunization programmes can use implementation research in three main ways. Firstly, immunization programmes can use validated, and theory-informed implementation determinants frameworks to explore and gain a deeper understanding of the implementation contexts of vaccination activities, and to identify factors that are responsible for implementation success or failure.²⁸ Examples of such frameworks include Consolidated Framework for Implementation Research (CFIR) and Theoretical Domains Framework (TDF).^25,29 Secondly, immunization programmes can use tailored, context-appropriate and context-relevant implementation strategies to address identified implementation barriers of vaccination activities so as to improve the performance of the overall immunization programme.³⁰ Finally, immunization programmes should drive sustainability of useful and effective implementation strategies to maintain optimal performance of the immunization programme across communities. The Practical Robust Implementation and Sustainability Model (PRISM) is a good example of a framework for integrating successful implementation strategies into routine programme settings, especially quality improvement.³¹ Figure 2 is an illustration that highlights the role of implementation research in optimizing the uptake of nationally recommended vaccines along the vaccine implementation spectrum.

Figure 2. Conceptual framework of the role of implementation research along the vaccine implementation spectrum.

In 2015, Alliance for Health Policy and Systems Research (AHPSR) began to support embedded implementation research in immunization programmes in several low- and middle-income countries, some of which are in the WHO African region.³² Embedded implementation research focuses on enhancing implementation in real world settings through collaborative partnership and involvement of decision makers.³³ AHPSR uses an agile model where the decision-makers themselves lead the research process from research question formulation to analysis and interpretation, as this can fast track translation of findings into policies.³² Some of the research questions in past projects have focused on pertinent issues such as data quality, defaulter tracking, vaccine hesitancy, service utilization among others.³²

However, implementation research can be used to support broader practice change in immunization systems from exploration to scale-up.³⁴ The specific kind of practice change that is needed to improve immunization equity and make progress toward IA2030 within countries is context dependent, and immunization stakeholders within those settings will need to collaboratively identify what is appropriate for their communities. However, as shown in Figure 3, there are some potential low hanging opportunities that are worth considering if they are an appropriate match for the gaps identified during context assessment. They include:

1. Integrating childhood vaccinations with other health services in public and private health facilities to improve access and reduce missed opportunities. If vaccination services are offered at every service delivery points in health facilities, and a policy to review the vaccination history of every child who had encounter with the facilities (regardless of the reason) is instituted, the number of children that will be vaccinated is likely to increase. A follow-up mechanism should be set up to prevent default.

2. Scaling up vaccination services provision to cover all public and private health facilities. In resource constrained settings, a hub-and-spoke model can be used to link health care facilities without capacity to offer vaccination services (spokes) with a facility that offers vaccination services (hub).³⁵ Spoke sites can at least institute active screening of children to identify unimmunized and underimmunized children, and escort them to where they can get vaccination services.

3. Expanding vaccination services through the informal health sector in communities where zero-dose children are concentrated and health services are unavailable like conflict zones, urban slums and hard-to-reach rural areas. A hub-and-spoke model can also be used to integrate informal healthcare providers into the primary health care system to ensure quality.

4. Leveraging existing community health workers and upskilling them to offer vaccination services routinely alongside other health care services.

Figure 3. Some proposed transitions to expand access to vaccination services.

These suggested practice changes focus on the structures that are responsible for the delivery of vaccines, and should not be tested in isolation but as part of a package. This is because the implementation determinants that influence implementation outcomes in real world settings are usually multilevel and multifaceted, as such, multicomponent implementation strategies might be more useful.³⁶

Rigorous scientific methods should be used to test the effectiveness of multicomponent implementation strategies in improve performance of immunization programmes across diverse implementation contexts. Depending on resource availability, these studies can either use quasi-experimental or hybrid designs.^37,38 The main difference between the two designs is that in quasi-experimental studies, the units or groups are not randomized, while in hybrid designs, randomization is performed.^37,38 But both of these research approaches emphasize external validity, and are therefore suitable for informing scale-up in other complex settings.^37,38 There are several examples of quasi-experimental designs, some of which are pretest-posttest and interrupted time series.³⁸ When using this type of design, it is advisable to include comparators in order to improve the strength of the evidence.³⁸ Hybrid designs are mainly of three types.³⁷ A type 1 hybrid design is primarily focused on generating evidence on the effectiveness of an intervention, even though implementation is being monitored.³⁷ The type 2 hybrid design simultaneously monitors both intervention effectiveness and implementation outcomes at the same time.³⁷ Finally, in the type 3 hybrid design, the primary focus is on evaluating implementation, even though intervention effectiveness is being tracked.³⁷ Overall, substantial financial investment is required to increase implementation research in immunization programmes.

Implementation science training for immunization practitioners

The use of theories and frameworks is sine qua non to implementation research, and to ensure effective and proper use, training of immunization practitioners especially programme managers at national and subnational level in implementation science is paramount. Since implementation science is a relatively new field of study, training is a worthwhile investment to ensure that people are conducting actual implementation research and not general health service research. There are several implementation science capacity-building programmes around the world,³⁹ and through partnerships and collaboration, these institutions can be engaged to train immunization stakeholders.

Conclusion

The human cost that is associated with implementation failure in immunization programmes is significant and unjust, and therefore effective programme implementation deserves unequivocal urgent action so that the global health community can live up to its promise that vaccination is a human right. This will require substantial investment in vaccine implementation research. Among other things, countries should be supported to institute policy reforms that will ensure the highest standards of research ethics so that they can maximize the full potentials of implementation science in transforming their immunization programmes and the overall health system.

Author contribution

A.A. conceptualized this paper. A.A.A., D.N., R.I.J. and C.S.W. reviewed the original draft. A.A.A., D.N., R.I.J., and C.S.W. were involved in writing and reviewing the final draft.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.