Prevalence and dynamics of missed opportunities for vaccination among children in Africa: applying systems thinking in a systematic review and meta-analysis of observational studies

<b>Objective</b>: To estimate the prevalence of missed opportunities for vaccination (MOV) among children aged 0–23 months attending health-care facilities in Africa and explore the factors responsible for MOV using systems thinking. <b>Research design and methods</b>: We conducted a systematic review and meta-analysis of studies reporting the proportion MOVs. Five electronic databases were searched. A random effects model was fitted to obtain pooled estimates of MOV and a causal loop diagram (CLD) was constructed to explore the dynamics of the causes of MOV. MOV was defined as any contact with health services in Africa, by an unvaccinated or under-vaccinated child, aged 0–23 months, who is eligible for vaccination and free of any contraindication, which does not result in vaccination. <b>Results</b>: Four hundred and twenty-one publications were found, of which 20 studies from 14 countries were included. The pooled prevalence of MOV was estimated to be 27.26% (95%CI: 18.80–36.62). A CLD with seven reinforcing and two balancing loops were constructed. <b>Conclusion</b>: Our findings suggest that about one in every four children under the age of two years who visited health facilities in 14 African countries missed the vaccination they were eligible to receive. To enable continent-wide estimates, more MOV assessments are required.

<b>研究目标</b>：评估非洲0~23月龄就诊于医疗机构的儿童疫苗接种遗漏机会（missed opportunities for vaccination, MOV）的流行率，并运用系统思维探究MOV的相关影响因素。<b>研究设计与方法</b>：本研究针对报告MOV占比的相关研究开展系统综述与元分析。检索了5个电子数据库，采用随机效应模型得到MOV的合并估计值，并构建因果环路图（causal loop diagram, CLD）以探究MOV致病因素的动态关联。MOV的定义为：非洲地区0~23月龄、符合疫苗接种指征且无接种禁忌证的未接种或接种不足儿童，在与医疗机构发生接触时未获得疫苗接种。<b>研究结果</b>：本研究共检索到421篇文献，最终纳入14个国家的20项相关研究。MOV的合并流行率估计为27.26%（95%置信区间：18.80~36.62）。构建了包含7个强化环路与2个平衡环路的因果环路图。<b>研究结论</b>：本研究结果显示，在14个非洲国家的医疗机构就诊的两岁以下儿童中，约四分之一符合接种条件的儿童未能获得应有的疫苗接种。为获取全非洲范围的流行率估计数据，仍需开展更多MOV相关评估研究。