Parent-reported barriers and facilitators to second or subsequent dose uptake in childhood vaccination: A mixed-methods systematic review protocol

<ns5:p> Background Completion of childhood vaccination schedules is essential to prevent childhood morbidity and mortality and to protect population health. Despite improvements in first-dose coverage globally, uptake of second or subsequent dose vaccines remains suboptimal. Parents serve as the primary decision-makers for childhood vaccination, with both modifiable and non-modifiable factors influencing vaccination uptake. However, it remains unclear what barriers and facilitators specifically affect second or subsequent vaccine dose uptake. The objective of this mixed-methods systematic review is to identify and integrate the existing evidence regarding parent-reported barriers and facilitators to second or subsequent dose uptake in childhood vaccination. Methods This mixed-methods systematic review will follow the methodological guidance from the Joanna Briggs Institute (JBI) Manual for Evidence Synthesis. This review will include both published and unpublished literature employing quantitative, qualitative, and mixed-method approaches. A comprehensive and systematic search of electronic databases will be conducted, including PubMed, CINAHL, Scopus, PsycINFO and Cochrane Library. No search limits on date or language of publication will be applied. Searches for grey literature or research published outside of the indexed journal article format will be searched to supplement the electronic database searches. The findings will be reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses. Discussion This mixed-methods systematic review will present integrated findings of parent-reported barriers and facilitators to second or subsequent dose uptake in childhood vaccination. The findings are expected to inform the design of targeted, evidence-based interventions aimed at improving second or subsequent dose vaccine uptake and overall childhood vaccination coverage. In doing so, the review will support global immunisation priorities, including the World Health Organisation’s Immunisation Agenda 2030. <ns5:bold>Systematic review registration number:</ns5:bold> PROSPERO 2026 CRD420261324738. </ns5:p>