Effectiveness and feasibility of three types of parent reminders to increase adolescent human papillomavirus (HPV) vaccination

Human papillomavirus (HPV) vaccines are a breakthrough in cancer prevention, protecting against cancers caused by HPV types. Despite recommendations for routine vaccination of 11-12-year-olds, vaccination rates remain low (only 67% initiated and 45% completed the series by age 13 in 2019). Parent reminders, being low-cost and scalable, have been used to improve childhood immunization rates. However, the HPV vaccine requires multiple doses and faces greater parental hesitancy, posing challenges. This study focuses on understanding the feasibility, effectiveness, and implementation of different HPV vaccine reminder types in resource-limited settings like Federally Qualified Health Centers (FQHCs). Prior research has shown modest improvements in HPV vaccination using various reminder methods (letters, phone calls, texts, emails), but often lacked randomized designs and focused on resource-rich settings. This study aimed to evaluate the effectiveness and implementation of three parent reminder types (mailed letters, robocalls, text messages) on HPV vaccine dose completion among 12-year-olds in a large, multi-site FQHC in Los Angeles County. The hypothesis was that adolescents whose parents received reminders would have higher vaccination rates than those in usual care, with text messages being the most feasible.

Previous studies evaluating parent reminder and recall messages, including letters, phone calls, text, and email messages, have demonstrated modest improvements in HPV vaccination rates among adolescents. However, many studies employed non-randomized designs and were conducted in various settings such as public health agencies, managed care settings, or private practices. Little research has focused on low-resource settings or compared the effectiveness and implementation of multiple reminder types simultaneously. Existing studies showed varying effects, with some showing stronger effects with more follow-up messages and incorporating parent preferences. Many studies used individual randomization, limiting generalizability to system-level implementation. This study aimed to address these gaps by using a quasi-experimental design and implementing the intervention within existing clinic infrastructure.

This quasi-experimental study evaluated the effectiveness and implementation of three clinic-level reminder systems for HPV vaccine next-dose (dose 1 or 2) completion among adolescents (12-year-olds) at a large, multi-site FQHC in Los Angeles County. Six clinics were paired based on baseline HPV vaccination rates, patient population size, and location. Within each pair, one clinic was randomly assigned to usual care, and the other to one of three reminder interventions: mailed letter, robocall, or text message. Eligible patients were 12-year-olds due for an HPV vaccine dose. The reminder intervention was implemented between November and December 2016. The FQHC's call center generated mailed letters and robocalls; a third-party vendor sent text messages. Reminders were delivered in patients' preferred language. Up to two reminders were sent per patient. Usual care clinics received no targeted interventions to improve HPV vaccine uptake beyond routine practices. Data were collected from electronic medical records and population health management systems. The primary outcome was next-dose vaccination. Logistic regression models were used to analyze the data, accounting for health center as a covariate in most models.

The study sample comprised 877 12-year-olds (47% female, >85% Latino). Overall, 23% of adolescents in any reminder condition received the next HPV vaccine dose compared to 12% in the usual care group (11 percentage point [pp] advantage, p = 0.046). Stratified analysis showed a significant effect only for text message reminders (11 pp advantage, p = 0.036). A significant effect was observed for boys in any reminder condition (15 pp advantage, p = 0.006), but not for girls (6 pp advantage, p = 0.829). Regarding implementation, robocalls had the lowest successful delivery rates (Figure 2). Text message delivery exceeded 80%, while mailed reminders also had high success rates. Opt-out rates for text messages were low (2%). Successful delivery was defined by absence of feedback indicating failure (e.g., bounce-back for text, returned mail, unanswered robocalls).

This study confirms the effectiveness of parent reminders in increasing adolescent HPV vaccination rates, particularly text message reminders. The effect size of text message reminders (11 percentage points) is consistent with prior interventions among publicly insured adolescents. Stronger effects have been reported in studies using more follow-up messages and considering parent preferences. This study's quasi-experimental design, assigning clinics to interventions, provides insights into real-world implementation feasibility. While robocalls showed non-significant improvement, their low reach (one-third of reminders unanswered) and potential for being blocked highlight their lower feasibility. The preference for text messages over phone calls or mailed reminders has been noted in prior qualitative research. The significant improvement in vaccination rates among boys but not girls may be due to differing levels of parental awareness and provider recommendations. This study's high implementation feasibility, especially for text and mailed reminders, contrasts with lower rates reported in other studies. However, the 'successful delivery' measure doesn't capture actual reminder receipt by parents.

This study supports the use of parent reminders, particularly text messages, to improve adolescent HPV vaccination. Future research should confirm these findings in larger samples and compare reminders to other clinic-based vaccine promotion strategies, considering cost-effectiveness and implementation challenges. Further investigation into the reasons for gender differences in response to reminders is warranted.

The study focused on one FQHC system with a predominantly Latino population, limiting generalizability. The study only included 12-year-olds, excluding older adolescents or adults eligible for catch-up vaccinations. The sample size limited direct comparisons between reminder types. The implementation measure was relatively crude, not capturing actual reminder receipt by parents.