Clin Infect Dis. 2026 Apr 12:ciag219. doi: 10.1093/cid/ciag219. Online ahead of print.
ABSTRACT
BACKGROUND: Immunosuppressed individuals face higher risk of severe influenza complications, yet vaccination coverage remains low. We aimed to assess the effect of electronic letter-based nudges on influenza vaccination uptake by immunosuppression status.
METHODS: We performed a participant-level pooled analysis of two methodologically harmonized, nationwide, pragmatic randomized clinical trials (NUDGE-FLU-2 and NUDGE-FLU-CHRONIC) conducted during the 2023-2024 influenza season. Adults aged ≥65 years (NUDGE-FLU-2) and adults aged 18-64 years with chronic conditions (NUDGE-FLU-CHRONIC) were included, with immunosuppression defined by an immunosuppressive diagnosis or a filled prescription for immunosuppressive therapy. Participants were randomized in a 2.45:1:1:1:1:1:1 ratio to usual care or one of six electronic letter interventions. The primary outcome was receipt of influenza vaccination by January 1, 2024, ascertained from nationwide administrative health registries. Effect modification by immunosuppression status was assessed using binomial regression.
RESULTS: Among 1,181,254 participants (mean age 67 years; 73,830 [6.3%] immunosuppressed), 66.1% were vaccinated. Any letter increased vaccine uptake compared with usual care (absolute difference, 2.79 percentage points; 95% CI, 2.60-2.98; p<0.001), with greater effect among immunosuppressed individuals (+4.12 vs +2.70 percentage points; pinteraction=0.002). In younger adults with chronic conditions, letter-based nudges increased vaccination rates by 11.7 percentage points overall and by 13.3 percentage points among those with immunosuppression (pinteraction=0.007). Among immunosuppressed individuals, nudging effects appeared greater for those with immunosuppressive conditions than for those receiving immunosuppressive treatment.
CONCLUSIONS: Electronic letter-based nudges increased influenza vaccination rates, with greater benefit among individuals with immunosuppression. These findings support implementation of low-cost, letter-based nudging strategies to improve vaccine uptake in this high-risk population.
PMID:41968745 | DOI:10.1093/cid/ciag219