Introduction Worldwide, suboptimal immunisation coverage causes the deaths of more than one million children under five from vaccine-preventable diseases every year. Reasons for suboptimal coverage are multifactorial, and a combination of interventions is needed to improve compliance with immunisation schedules. One intervention relies on reminders, where the health system prompts caregivers to attend immunisation appointments on time or re-engages caregivers who have defaulted on scheduled appointments. We undertake this systematic review to investigate the potential of reminders using emails, phone calls, social media, letters or postcards to improve immunisation coverage in children under five. Methods and analysis We will search for published and unpublished randomised controlled trials and non-randomised controlled trials in PubMed, Scopus, CINAHL, CENTRAL, Science Citation Index, WHOLIS, Clinicaltrials.gov and the WHO International Clinical Trials Platform. We will conduct screening of search results, study selection, data extraction and risk-of-bias assessment in duplicate, resolving disagreements by consensus. In addition, we will pool data from clinically homogeneous studies using random-effects meta-analysis; assess heterogeneity of effects using the (2) test of homogeneity; and quantify any observed heterogeneity using the I-2 statistic. Ethics and dissemination This protocol does not need approval by an ethics committee because we will use publicly available data, without directly involving human participants. The results will provide updated evidence on the effects of electronic and postal reminders on immunisation coverage, and we will discuss the applicability of the findings to low and middle-income countries. We plan to disseminate review findings through publication in a peer-reviewed journal and presentation at relevant conferences. In addition, we will prepare a policymaker-friendly summary using a validated format (eg, SUPPORT Summary) and disseminate this through social media and email discussion groups. Review registration number PROSPERO registration number CRD42014012888.
