Abstract
OBJECTIVE: Human papillomavirus (HPV) vaccine uptake remains suboptimal. Our stepped-wedge cluster randomized trial found that reminder-recall letters sent to parents of age-eligible children significantly increased vaccine uptake compared to usual care. Subsequently, we conducted a process evaluation to assess the mechanisms of the letter's effectiveness. This study evaluated who remembered the letter, use of provided resources, and child vaccination status. METHODS: This cross-sectional evaluation included data from parents (n = 1165) of adolescents ages 11-12 from six primary care practices who received letters about their child's HPV vaccination status. From 2018 to 2022, parents were mailed reminder-recall letters and then sent questionnaires 12-15 months after receiving the letter. Questionnaires asked if parents recalled the letter, whether their child received a vaccination and, if not, reasons for not vaccinating, and attitudes and beliefs about HPV vaccination. RESULTS: A total of 1165 of 1991 questionnaires were completed (59 %). Over half (58 %) remembered the reminder-recall letter. Compared to those not remembering the letter, those who did were significantly more likely to have had their child vaccinated (56 % versus 44 %, p < 0.05). Of those who remembered the letter but did not vaccinate, the majority reported misperceptions about their child being too young (26 %) or concerns about vaccine safety (20 %). Of those who did not remember the letter and did not vaccinate, the primary reason was not knowing the child was due for vaccination (27 %). CONCLUSIONS: Reminder-recall letters cued the majority of parents to complete HPV vaccination; however, vaccine misperceptions remain a challenge, indicating the need for additional communication strategies.