RESUMEN
BACKGROUND: The effectiveness of SMS reminders in improving vaccination coverage has been assessed previously, with effectiveness varying between settings. However, there are very few studies on their effect on the timeliness of vaccination. DESIGN: Unblinded, randomised controlled trial with blocked sampling. METHODS: 1594 Australian infants and young children were recruited to assess the impact of (1) SMS reminders only, (2) a personalised calendar, (3) SMS reminder and personalised calendar and (4) no intervention, on receipt of vaccine within 30 days of the due date. Outcomes were measured for receipt of vaccines due at 2, 4, 6, 12 and 18 months of age. A post-hoc assessment was also conducted of the impact of a new national "No jab No Pay" policy introduced during the trial, which removed philosophical objections as an exemption for financial penalties for non-vaccination. RESULTS: There was a statistically significant improvement in on-time vaccination only at the 12 month schedule point amongst infants who received SMS reminders alone (RR 1.09, 95% CI 1.01-1.18) or in combination with a personalised calendar (1.11, CI 1.03-1.20) compared to controls. This impact was limited to participants who had received one or more previous doses late. No statistically significant impacts of calendar interventions alone were seen. There was a high rate of on-time compliance amongst control participants - 95%, 86%, 80%, 74% at the 4, 6, 12 and 18 month schedule points respectively, which increased more than 10 percentage points after implementation of the "No Jab, No Pay" policy. CONCLUSIONS: SMS reminders are more effective in improving timeliness where pre-existing compliance is lower, but the 18 month schedule point appeared to be less amenable to intervention. Australia and New Zealand Clinical Trial Registration No. ACTRN12614000970640.