To assess the effects of behaviourally informed short message service (SMS) reminders on demand for human papillomavirus (HPV) immunisation.

Individually randomised, five-group, controlled parallel trial.

A country-wide trial in Georgia.

55 176 girls aged 10–12, the entire population of unvaccinated girls of this age in the country, for whom there existed caregiver contact details.

Girls were randomised into five arms (four with n=11 035, with one n=11 036). Caregivers of the girls in four of the arms (treatment groups) were sent different versions of an SMS reminder (SMSR), reminding them that the girl was due to receive the HPV vaccine. The control group was sent no SMSR.

The primary outcome was a girl’s HPV vaccination status at the end of the trial.

Girls and their caregivers were blinded to group assignment.

The number of participants analysed in the four treatment groups was 10,784, 10,802, 10,794 and 10,820, with 10 828 analysed in the control group.

Each of the SMSRs was more effective than the control (no reminder) in encouraging HPV vaccination. Girls whose caregiver(s) were sent version 3 had 65% greater odds of receiving the vaccine relative to the control group (OR=1.65; 95% CI 1.38 to 1.97). Among girls whose caregivers received version 1, version 2 and version 4 of the SMS, the odds of receiving the HPV vaccine were respectively 42% (OR=1.42; 95% CI 1.18 to 1.70), 34% (OR=1.34; 95% CI 1.12 to 1.61) and 35% (OR=1.35; 95% CI 1.13 to 1.62) higher compared with the girls in the control arm.

We find a positive and statistically significant effect for each version of the SMSR, relative to the control condition.

NCT05536674.