Realist Synthesis of the International Theory and Evidence on Strategies to Improve Childhood Vaccination in Low- and Middle-Income Countries: Developing Strategies for the Nigerian Healthcare System

Although multiple strategies have been used to improve national immunisation coverage in Nigeria, there was a gradual decline in the third dose of diphtheria, tetanus, and pertussis-containing vaccine (DTP3) after peak coverage in 2009, and the estimated DTP3 coverage of 42% remained stagnant from 2015-2017. Using a realist synthesis approach, this study analyses strategies used to improve childhood vaccine access and uptake in low- and middle-income countries (LMICs) in order to inform strategy development for the Nigerian healthcare system.

The researchers explain that Nigeria has major religious, cultural, and socioeconomic differences across its large population. Its citizens range from nomadic communities to hard-to-reach communities living in riverine areas, with many rural and urban communities in between. For a strategy to be successful within any community, it has to consider the community's context in order to address its peculiar needs, and on a scale sufficient to make an impact, as not all interventions will have the same effects in all settings.

Realist synthesis, which involves the systematic review of primary studies, was deemed suitable for this research because it enables "contextually-sensitive assessment of the effectiveness of interventions, which can be used to build middle-range theories about likely levels of effectiveness in other comparable settings." Having searched 9 databases of relevant articles, the researchers included 27 articles in that were published after 1996. (The process and criteria are outlined in the article.)

Before sharing the results of the review, the researchers point out that demand-side strategies are usually based on the assumption that factors such as ignorance, financial constraint, and poor recall of vaccination schedule influence non-uptake of vaccination. Conversely, supply-side strategies are based on the assumption that health workers' lack of knowledge and skills, poor supportive supervision, and lack of motivation are the main factors affecting the quality of care provided to children, resulting in low vaccination coverage. Supplementary file 1 contains a description of the articles included in the review, categorised according to their intervention type, with brief descriptions of settings, participants, methods, and outcomes of each intervention. In short, interventions used in LMICs to improve vaccination coverage are categorised as follows:

• Communication/education - These approaches are based on the belief that effective communication and education will increase vaccine uptake by raising awareness, creating and sustaining demand, preventing or dispelling misinformation and doubts, encouraging acceptance of and participation in vaccination services, and facilitating more rapid reporting of disease cases and outbreaks. It is assumed that providing the right information (e.g., through one-on-one sessions with mothers) will result in people making rational decisions and following through with appropriate action (behaviour change). Some authors find that sessions with shorter duration and more focused content will produce better retention and behaviour modification. Also, some believe that communication will work through the use of influential persons in communities to pass across vaccination messages. For example, in Bauchi State, Nigeria, as well as in Iraq, Pakistan, and Afghanistan, which are predominantly traditional Muslim societies, the education and engagement of traditional and religious leaders as advocates for immunisation helped enhance communication with the community, thereby increasing acceptance of vaccination. Overall insights: Communication and educational interventions were successful within a variety of contexts. They are likely to be most effective when they: utilise influential leaders, include cost-benefit discussions, and increase awareness of health entitlements.
• Reminder-type interventions - This approach assumes that the reason for reduced uptake is forgetfulness, and that enhancing recall of immunisation appointment dates, times, and venues could increase uptake. It considers reminders to be a valid mechanism for communication between parents and healthcare providers, which can be harnessed to educate parents on the importance of vaccine completion and to encourage them to return for their vaccination appointments (thereby sharing some underlying assumptions of communication/education interventions). Overall insights: The results show that SMS (text messaging) reminders are likely to be successful in contexts with 100% mobile coverage where each household has a functional mobile phone, through text messages in the local language. Reminder-type immunisation cards appear to work well in rural and urban settings by increasing visibility of the next immunisation date.
• Incentives - Incentives work through external motivation according to the theory of motivation. It is believed monetary incentives will raise awareness about beneficial behaviour and enable people make the right choices by covering the financial and opportunity costs that would otherwise have accrued to them and prevented vaccination uptake. Some authors believe adding conditions to these monetary transfers will ensure compliance and result in immunisation completion. Some believe that non-monetary incentives such as raw lentils and metal plates will provide small benefits that might overcome little barriers that hold the key to large improvements in immunisation rates. Overall insights: Incentive-based strategies appear to be most effective when designed for hard-to-reach and economically poorer communities. A common theme was that the effect could not be clearly attributed to the incentives because the control group also demonstrated improvement, or alternatively that there was an improvement which was either not sustained or was insufficient to attain desired vaccine coverage levels. Most of the articles on incentive-based strategies did not rigorously model cost and benefits.
• Social/community mobilisation - It is believed that social mobilisation efforts addressed to the grassroots will reach underserved populations through supplementary immunisation activities (SIAs) to reach them at the community level and will combat rumours against vaccination. Also, home visits by non-health workers (NHWs) can not only enable eligible children be identified and referred for immunisation but provide an opportunity for direct personal communication (dispelling myths, educating mothers) that can result in higher immunisation uptake. In addition, it is assumed that any intervention in people's homes that is tailored to meet their needs, if implemented in a sensitive way, is likely to have a positive impact. Overall insight: NHWs in collaboration with healthcare providers have an important role to play in improving vaccination coverage.
• Provider-directed strategies - These strategies assume that bottlenecks lie principally with those charged with provision of vaccines. Therefore, supportive supervision can enable staff to carry out their duties effectively by providing guidance, support, motivation and assisting staff to become more competent in their work. Also, staff training can improve immunisation knowledge and skill amongst staff, and thereby reducing missed opportunities and drop-outs. Overall insight: Provider-directed strategies appear to be effective in contexts with poor health worker performance and free vaccination at the point of delivery, and when they incorporate health worker training and supportive supervision.
• Health service integration - The basis for this intervention is that routine immunisation (RI) programmes have the greatest and most equitable coverage of all childhood preventive programmes in the developing world, and also provide multiple health contacts with mothers and their children. Hence, the reach of other health interventions can be extended by integrating them with RI. Also, the availability of other health interventions such as hygiene kits or insecticide-treated nets could act as incentives to increase vaccination coverage. Overall insights: Evidence shows that for integration to be mutually beneficial to both programmes, the programme being hinged unto RI must also be able to stimulate public interest; otherwise, it could be counterproductive to the continued success of RI.
• Multi-pronged strategies - The multi-pronged programmatic approach is believed to pull together the benefits of different proven interventions that address both the demand and supply aspects of the vaccination coverage problem in order to produce a complete package that can improve immunisation coverage. Overall insights: For multi-pronged immunisation packages to be utilised routinely in many settings, it appears necessary to identify which combination of interventions produces the greatest impact at the lowest cost, so that implementation can be sustainable in the long run. Multipronged interventions appear to be successful amongst hard-to-reach communities if and when they incorporate the package into already existing health services.

The strategies that appeared most likely to be effective in the health contexts of contemporary Nigeria include: implementing communication and educational interventions (especially those engaging influential religious or traditional leaders); employing informal change agents; and monitoring and evaluation to strengthen communication. Programmes using reminders and social mobilisation were generally successful within some contexts. "Capacity building is another important challenge in Nigeria that cannot be over-emphasised as it can help to prevent missed opportunities and drop-outs, improve health workers' knowledge, attitude and practice, and improve data recording and reporting." By contrast, the use of monetary incentives in Nigeria is not supported by the evidence, although further research and evaluation is needed. The integration of other interventions with RI to improve uptake was more effective when the perceived value of the other programme was high. Adoption of multipronged interventions for hard-to-reach communities was beneficial, though such an approach would need to be adapted to meet the population's needs, bearing in mind the cost-effectiveness profile of each intervention within the immunisation package.

The majority of the interventions discussed for RI may be beneficial in immunisation campaigns also. As with RI, engaging influential leaders to legitimise and promote the vaccination agenda and providing focused immunisation messages in the caregiver environment may be beneficial during immunisation campaigns. Specifically for campaigns, communication can be enhanced through the use of town hall meetings, town criers, television announcements, radio jingles, hand bills, and posters. Furthermore, the importance of social mobilisation through NHWs as community mobilisers was demonstrated in India and may effective in Nigerian vaccination campaigns.

The researchers stress that caution should be exercised because of varying levels of published evidence in respect of each intervention type and a relative lack of the rich description required to conduct a full realist analysis.

That said, the researchers conclude that the realist synthesis framework "was particularly useful in enabling each intervention's outcomes to be situated within its context. It generated realistic information on how and in what contexts strategies to improve childhood vaccinations work. Due to its focus on mechanisms of change, there was greater analytic power to explain the heterogeneity of results which enhances its transferability in terms of policy and practice."