Short Message Service Reminders to Parents for Increasing Adolescent Human Papillomavirus Vaccination Rates in a Secondary School Vaccine Program: A Randomized Control Trial

In Victoria, Australia, the human papillomavirus (HPV) vaccine is delivered within a state-wide secondary school vaccine programme; coverage rates remain below the 80% target required for herd immunity. Alongside regulatory approaches to optimising vaccination rates, behavioural science offers strategies for policymakers to achieve their health goals, for example, parent reminders. In Victoria's school-based programme, a consent card and information booklet are sent home to all parents and returned to the school at the beginning of the year. Parents are also reminded about the vaccine session via the school newsletter/online parent portal in the weeks leading up to each school visit. This study aimed to test the hypothesis that sending a short message service (SMS) reminder to parents who had consented to their child's receiving the HPV vaccine would lead to greater uptake of the vaccine. The secondary aim was to assess the effect of self-regulatory versus motivational message content in the SMS.

Research has shown that the effect of reminders may depend on the content of the message. One study found that a simple request to "make a plan" for getting a flu shot increased vaccination rates within an organisational setting. Another approach is to emphasise the individual's susceptibility to disease, a motivational strategy based on the Health Belief Model. One study revealed an increase in measles vaccinations by informing parents that children most at risk of measles are those that have not been immunised. Together, these behavioural techniques provide an opportunity to increase the efficacy of reminders. However, neither of these strategies has been trialed on adolescent samples, nor has their comparative effect been tested.

For the present study, a randomised control trial design was used across 31 schools within 7 local government areas. Parents of 4,386 consented adolescents were randomised into 3 study conditions:

• Motivational SMS: "Reminder from [name of provider]: [name of child] has a vaccine appointment at school this [day of week]. Vaccine preventable diseases are still a problem in the community and children most at risk are those that have not been immunised. Please contact xxxx xxxx if your child cannot attend."
• Self-regulatory SMS: "Reminder from [name of provider]: [name of child] has a vaccine appointment at school this [day of week]. Make a plan now for how [name of child] will get to school on-time on immunisation day. Please contact xxxx xxxx if your child cannot attend. Thank you."
• No SMS.

Only one reminder was sent per student, and the providers did not assess if the SMS was successfully delivered to the recipient. Follow-up extended beyond the final school visit to the end of the calendar year to capture those who may have attended an end-of-year catch-up vaccination session at a local government office (available to any student who may have missed a vaccine during the year).

On the day of the final school visit, 85.71% of consented students in the control condition received the HPV vaccine, compared with 88.35% (2.64% point increase) in the motivational message condition, and 89.00% (3.29% point increase) in the self-regulatory message condition. Both intervention messages were similarly effective at increasing vaccination rates. This effect was maintained in the extended follow-up period.

There were no noticeable gender differences for any of the outcome variables. For example, in both the male and female participants, the vaccination rate (any dose) was higher in the motivational (male 87.86%; female 88.68%) and self-regulatory (male 86.90%; female 90.12%) message conditions than the control condition (male 84.19%; female 86.34%).

The researchers note that success of SMS reminders is facilitated by almost universal access to and frequent use of mobile devices. Currently, however, not all schools provide parents' mobile phone numbers to local government, and few provide a full set of student data in a readily usable format. For such an initiative to be adopted state-wide, additional efforts would need to be made to address existing data quality issues.

Six complaints were received in relation to this trial, all pertaining to the self-regulatory message. It may be that parents/guardians perceived that the self-regulatory message implied they were disorganised; however, this is speculative. The discrepancy between the complaint rate of the self-regulatory message and the motivation message and the lack of any statistically significant difference between the response rates of these messages suggests that the motivational message should be used in further SMS messages.

Although this trial lifted vaccination rates, approximately 10% of students in the intervention conditions did not receive any dose of the HPV vaccine. Although it is possible that students may have received the vaccine elsewhere, it is unlikely to account for all these students. A number of factors may account for why a student with consent missed the vaccine; however, anecdotally, the primary reason is that students are not at school on the day of vaccination, and, therefore, additional intervention approaches that seek to ensure student attendance may further help reduce this gap. Scope also exists to increase vaccine uptake by increasing consent card return rates. Approximately 20% of students did not have consent within the school programme, and yet, vaccination refusal rates are estimated to be as low as 2% overall in Australia. Finally, the findings suggest that the reminders primarily took effect among individuals who had a history of noncompliance with the vaccine. This suggests that vaccine completion rates would be increased if the reminders were used for the first/second school visits, so these individuals stay on-track to complete the vaccine schedule.

In conclusion, this study found that SMS reminders to parents/guardians are an effective strategy for encouraging adolescents to receive the HPV vaccine within school-based vaccine programmes. The results demonstrate to policymakers the potential of harnessing new media and behavioural science interventions to supplement traditional policy approaches, such as regulation, to optimise vaccination uptake. However, further research could be useful to determine the scalability and precise parameters required for successful state- and nation-wide reminder programmes and to determine if using an SMS reminder is effective within independent and special/language schools, which were not included in this study.