SMS reminders to improve the uptake and timeliness of the primary immunisation series in infants: a multi-centre randomised controlled trial

Background Immunisation timeliness continues to present challenges to achieving optimal vaccine coverage in infancy, particularly in disadvantaged groups and Australian First Nations infants. We aimed to determine whether a tailored, educational SMS reminder improves the timeliness of immunisation in infants up to seven months of age. Methods A pragmatic, three-arm, parallel-group, randomised controlled trial of immunisation reminders was conducted in two First-Nations-specific primary health care centres and two public hospital antenatal clinics in South East Queensland, Australia. Live-born infants of mothers enrolled during pregnancy were randomised at birth and followed to eight months of age. One group received a simple SMS reminder at two weeks before, the week of, and two weeks after the due date for immunisation at two, four and six months of age. The second group received a tailored SMS with an educational message at two weeks before and on the date immunisations were due; those not immunised two weeks following the due date were offered support to immunise the baby. Controls received no intervention or contact until the baby turned seven months of age. The primary outcome was the proportion of infants age-appropriately vaccinated at seven months of age as recorded on the Australian Immunisation Register. Secondary outcomes included vaccination status at three and five months of age. Results Between 30 May 2016 and 24 May 2018, one hundred and ninety-six infants (31% First Nations infants) were randomised. At seven months of age, 54/65 (83.1%) infants in the educational SMS ± additional support group (ESMS±S) were age-appropriately immunised, compared to 45/64 (70.3%) in the simple SMS group and 45/67 (67.2%) in controls. Differences were most marked at five months of age: ESMS±S 95.5%; simple SMS 73.4%; controls 75.8%. The difference between the ESMS±S group and the other two groups at seven months of age was no longer apparent when those who received additional support beyond the SMS were assumed to have not been vaccinated if that support had not been received. Discussion A tailored SMS reminder system using an educational message and with provision of additional support to mothers is more effective in improving immunisation timeliness in infants at three and five months of age than a simple message and no intervention. The additional support was required at seven months of age in order to achieve higher coverage in the ESMS±S group.