Exploring supplemental immunization strategies to reach zero-dose children in low- and middle-income countries: a...

Nationwide measles immunization campaigns are resource-intensive yet can fail to reach the same children who are not reached by routine immunization services. Alternative approaches to better reach missed communities and improve efficiency focus on identifying and reaching unvaccinated, "zero-dose" children. Understanding the scope and impact of these strategies can inform approaches to fill immunity gaps and reduce measles disease burden.

We conducted a scoping review to map the existing literature on supplemental strategies used to reach zero-dose or under-vaccinated children in low- and lower-middle-income countries (LLMICs).

Our review focused on the "reach" component of the Identify-Reach-Monitor-Measure-Advocate (IRMMA) framework. We included literature describing vaccination interventions for measles-rubella, polio, and the Essential Program on Immunization (EPI) in LLMICs published from 2010 to 2021 in multiple languages. We excluded papers that solely focused on non-selective national vaccination campaigns.

We searched peer-reviewed databases (PubMed, WorldWideScience, and Scopus) and gray literature in World Health Organization (WHO) regional databases, the WHO Institutional Repository for Information Sharing, and John Snow, Inc. resource libraries.

Screening and extraction were conducted in Covidence. We iteratively coded, classified, and analyzed extracted data. Interventions were classified into the IRMMA framework categories: demand generation, human resources, supply chain, and service delivery.

Of 9450 articles screened, 185 met criteria for inclusion in the final analytic set. Strategies consisted of enhancements to the routine immunization program, with service delivery being the most frequent, followed by demand generation. Many studies described the integration of multiple strategies, offering opportunities to maximize reach and impact.

The vaccination strategies other than campaigns described in this review have been implemented in multiple countries; some demonstrate greater potential to reach zero-dose and under-vaccinated children. In the face of an evolving funding environment, prioritizing interventions that are most likely to reach unvaccinated children is key.