Interventions to improve pre-school vaccination timeliness: a systematic review

BACKGROUND: Improving the timeliness of pre-school vaccinations (children aged 0 to 5 years) is an important public health goal to prevent outbreaks and maximise protection during early childhood. Multiple studies have highlighted the need for effective public health interventions to improve timely vaccination, and consequently the overall effectiveness of vaccination programmes. We aim to synthesise evidence on vaccination timeliness interventions and subsequently provide recommendations to improve pre-school vaccination timeliness in England. METHODS: We conducted a systematic review of randomised controlled trials (RCTs) and non-randomised studies. Studies were eligible if they were conducted in high-income countries and evaluated an intervention to improve timeliness of any pre-school vaccination on the United Kingdom (UK) national childhood vaccination schedule. Five databases and grey literature were searched to February 2025. Risk of bias was assessed using Cochrane risk of bias tools. Data were analysed using random-effects meta-analyses and synthesis without meta-analysis (using effect direction plots). RESULTS: Of the 10,385 records from database searches and 1490 records from citation searches, 33 studies were eligible (15 RCTs, 18 non-randomised studies). Most studies were conducted in the USA (n = 24) and reported on the timeliness of multiple pre-school vaccines (n = 23). Twelve studies (36%) were judged as serious or critical risk of bias, eleven at moderate and ten at low risk. Various intervention groups were identified: call-recall (n = 10), quality improvement (n = 9), education (n = 5), multicomponent (n = 5), combination vaccines (n = 2), communication (n = 1) and vaccination schedule change (n = 1). We found limited evidence from a small number of studies of a potential beneficial effect of combination vaccines, communication, quality improvement, education and schedule change interventions. CONCLUSION: We identified several possible interventions to improve pre-school vaccination timeliness. However, we found limited quantity and quality of evidence on this topic. We recommend further high-quality studies evaluating interventions to improve vaccination timeliness in England, and application of consistent vaccination timeliness definitions.