"How" Versus "Why" Messaging to Increase Uptake of Booster Vaccination Against COVID-19: Results of a Pragmatic Randomized Trial.

BACKGROUND:Messages aimed at increasing uptake of vaccines have been modestly successful, perhaps in part because they often focus on why individuals should receive a vaccine. Construal Level Theory posits that messages emphasizing "how" to get a vaccine may be more effective at encouraging vaccination than emphasizing "why." This message framing may be particularly important for COVID-19 booster acceptance. OBJECTIVE:To determine if pre-visit patient portal messages designed using Construal Level Theory increase rates of COVID-19 booster vaccination. DESIGN AND INTERVENTIONS:This 3-arm randomized trial was conducted across three large, diverse primary care clinics in Massachusetts between February and May 2022, testing the impact of "how" versus "why" framed pre-visit messages versus no messages ("usual care"). Messages were sent by patient portal two business days before a visit. PARTICIPANTS:Adults with upcoming primary care visits who had electronic health record evidence of receiving their initial COVID-19 vaccination series but not a booster dose. MAIN MEASURES:Receipt of a COVID-19 booster vaccination after the message was sent through the visit date (primary outcome) or 6 weeks (secondary outcome). KEY RESULTS:A total of 3665 patients were randomized (mean age: 53.5 years (SD: 17.3), 59% female, 65.2% White, 26.6% Hispanic), with 1249 to "how" 1199 to "why," and 1217 to usual care arms. Except for clinic and preferred language, characteristics were well balanced across arms. Rates of COVID-19 booster were 13.6% (usual care), 11.7% ("how") (odds ratio (OR) "how" vs usual care: 0.87, 95%CI: 0.67-1.14), and 13.7% ("why") ("why" vs usual care: OR: 1.01, 95%CI: 0.81-1.28). At 6 weeks, "why" outperformed "how" for vaccination (OR: 1.26, 95%CI: 1.06-1.49), with no difference versus usual care. CONCLUSIONS:We found no differences on visit booster receipt after single pre-visit portal messages designed using Construal Level Theory. Further studies to identify effective messaging interventions are needed, especially as additional doses are recommended. CLINICAL TRIAL REGISTRATION:This trial is registered at clinicaltrials.gov, ID: NCT04871776 . Initial release occurred 04/30/2021.