Effectiveness of SMS Reminders to Increase Demand for HPV Immunisation: A Randomised Controlled Trial in Georgia

"[F]indings highlight the effectiveness of low-cost interventions, and add compelling evidence to support the use of 'reminder' messages for health services."



Behavioural science has been employed to develop and implement strategies to promote vaccine uptake in diverse settings globally. For example, there is growing evidence that nudges (in particular, those that are short messaging service (SMS)-based) can be a successful and cost-efficient method of encouraging vaccination and attendance at vaccination appointments. In Georgia, a transcontinental former Soviet state at the intersection of Eastern Europe and Western Asia, human papillomavirus (HPV) vaccine coverage remains low, and it fell over the course of the COVID-19 pandemic. UNICEF partnered with the Behavioural Insights Team (BIT) to explore behavioural barriers to HPV vaccination in the country and to develop and test solutions. The research team conducted a country-wide, large-scale randomised control trial (RCT) that included over 55,000 girls aged 10-12, representing the entire population of eligible unvaccinated girls of this age in the country.



The RCT tested the impact of 4 behaviourally-informed SMS reminder messages sent to these girls' caregivers, against a control in which no SMS reminder was sent. The messages were designed starting in January 2022, based on evidence from the behavioural science literature and the barriers to HPV vaccination in Georgia identified during earlier exploratory work (namely, the fact that caregivers did not previously receive reminders that their daughter was due for HPV vaccination). The 4 versions of the SMS reminder were as follows:

1. A short, simple reminder message with no additional information ("Your daughter is due her free human papillomavirus (HPV) vaccine which will protect her against cervical cancer. Contact your polyclinic today to arrange an appointment.") - This message uses: (i) timely prompt: This nudge is an intervention designed to influence behaviour without restricting choice; and (ii) defaults: The use of the language "Your daughter is due..." sets receiving the vaccine as the default option.
2. A reminder message with a link to the seduction of the National Center for Disease Control (NCDC)'s website that provides information about HPV vaccination - In addition to (i) timely prompt and (ii) defaults, this message uses messenger effects: People are often more receptive to messages from sources they believe to be authoritative and credible (e.g., the NCDC and its website).
3. A reminder message with the NCDC link and "reserved for her" framing (e.g., "Your daughter is due her free human papillomavirus (HPV) vaccine, which will protect her against cervical cancer. Her vaccine is reserved for her at the polyclinic.") In addition to (i) timely prompt, (ii) defaults, and (iii) messenger effects, this message uses loss aversion: When presented with information that a vaccine has been reserved for their daughter specifically, parents may feel more strongly encouraged to avoid missing a specific or limited opportunity.
4. A reminder message with the NCDC link and additional safety information about the HPV vaccine - In addition to (i) timely prompt, (ii) defaults, and (iii) messenger effects, this message uses social norm/social proof: This message provides social evidence that more than 118 million girls globally have safely received the vaccine without adverse effects; parents may be influenced by the idea that many others have had the vaccination, making it a socially accepted and recommended behaviour.

These SMS reminder messages were formulated by BIT and then translated into Georgian by the UNICEF Georgia country office, with specific care to maintain the integrity of the insights from behavioural science being employed.



The reminders were sent in September 2022, beginning a 62-day trial period. An intention-to-treat (ITT) logistic regression analysis examining the impact of treatment conditions on likelihood of being vaccinated during that 62-day period shows that 2,032 girls received the vaccine during the trial, a vaccination rate of 3.76%. This number varied from a rate of 2.4% for the control group to 4.7% for the group that were sent the "reserved for her" framing version of the SMS reminder, which was associated with the highest rate of vaccine uptake. Each version of the SMS reminder was more effective than the control at increasing uptake of the HPV vaccine, with "reserved" framing the most effective. If all caregivers in the trial had received this most effective message, the researchers estimate that an additional 488 girls would have been vaccinated, in addition to the 2,032 who received the HPV vaccine during the trial. In short, cumulatively, the 4 versions of the SMS reminder intervention were associated with a 75% relative increase in vaccination rate compared to the control (no SMS), at a marginal cost of US$0.15 (0.40 GEL at the time of writing) per additional vaccination observed.



In response to the findings, the NCDC and Ministry of Health in Georgia decided to (i) use the most effective version of the SMS (“reserved for her” framing) with all future cohorts of 10- to 12-year-old girls as they become newly eligible for vaccination and (ii) scale the use of this version of the SMS to their national catch-up campaign for unvaccinated 13- to 18-year-olds. Furthermore, these national health authorities have decided to expand the use of the "reserved for her" framing to their 2023 public health reminder campaigns for routine immunisation, screening for breast cancer, cervical cancer, colorectal cancer, and screening for hepatitis C.



In conclusion: "The results of this trial represent a novel contribution to the literature given they represent the application of an emerging tool (SMS reminders informed by behavioural science) to a new context where it had not previously been tested....Ultimately the SMS reminder intervention evaluated in this trial directly addresses only one (a lack of reminders for caregivers) of the many barriers to vaccination present in Georgia, and likely present in other contexts also. While the SMS reminders have demonstrated promising potential, it will also be necessary for public health authorities and policymakers to implement - and evaluate - interventions and policies that target other barriers to children receiving this and other potentially life-saving vaccines."

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