Carsten Schade Larsen | Search PubMed

PubMed2026

Electronic Nudges to Increase Influenza Vaccination in Immunosuppressed Adults Across the Age Spectrum: A Pooled Analysis of 2 Nationwide Randomized Trials.

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 2 methodologically harmonized, nationwide, pragmatic randomized clinical trials 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 1 of 6 electronic letter interventions. The primary outcome was receipt of influenza vaccination by 1 January 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% points; 95% confidence interval [CI], 2.60-2.98; P < .001), with greater effect among immunosuppressed individuals (+4.12 vs +2.70% points; Pinteraction = .002). In younger adults with chronic conditions, letter-based nudges increased vaccination rates by 11.7% points overall and by 13.3% points among those with immunosuppression (Pinteraction = .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 immunosuppressed individuals. These findings support implementation of low-cost, letter-based nudging strategies to improve vaccine uptake in this high-risk population. Clinical Trials Registration. NCT06030726 and NCT06030739.

Adolescent↗

PubMed2025

High-Dose vs Standard-Dose Influenza Vaccine and Cardiovascular Outcomes in Older Adults: A Prespecified Secondary Analysis of the DANFLU-2 Randomized Clinical Trial.

IMPORTANCE: The high-dose inactivated influenza vaccine (HD-IIV) has demonstrated superior protection against laboratory-confirmed influenza infection vs standard-dose IIV (SD-IIV); however, data regarding its effectiveness against cardiovascular (CV) outcomes are mainly from observational studies or specific high-risk groups. OBJECTIVE: To investigate the relative vaccine effectiveness (rVE) of HD-IIV vs SD-IIV against CV outcomes in the general older adult population in Denmark. DESIGN, SETTING, AND PARTICIPANTS: This was a prespecified secondary analysis of DANFLU-2, a pragmatic, open-label, individually randomized clinical trial (RCT) using nationwide administrative health registries in Denmark during the 2022/2023 to 2024/2025 influenza seasons. Older adults (age ≥65 years) were eligible for inclusion regardless of comorbidity. The trial design specified that if the primary end point was neutral, no hypothesis testing would be performed for secondary or exploratory end points. Data were analyzed from June 29 to August 12, 2025. INTERVENTIONS: Individual-level 1:1 randomization to HD-IIV or SD-IIV. Participants re-enrolling in additional seasons were rerandomized. MAIN OUTCOMES AND MEASURES: Severe CV outcomes were prespecified secondary and exploratory end points in the trial, occurring from 14 days after vaccination through May 31 the following year. RESULTS: A total of 332 438 participants (170 900 [51.4%] male; mean [SD] age, 73.7 [5.8] years) were randomized (166 218 to HD-IIV and 166 220 to SD-IIV), of whom 91 026 (27.4%) had a history of CV disease. HD-IIV did not significantly reduce the trial's primary end point of hospitalization for influenza or pneumonia. The incidence of hospitalization for any cardiorespiratory disease was lower in the HD-IIV group than the SD-IIV group (rVE, 5.7% [95% CI, 1.4% to 9.9%]; absolute difference, -0.13 [95% CI, -0.24 to -0.03] percentage points), and rVE did not differ by history of CV disease compared with no CV disease at baseline. Hospitalization for any CV disease occurred in fewer participants in the HD-IIV group than the SD-IIV group (rVE, 7.5% [95% CI, 1.5% to 12.5%]; absolute difference, -0.10 [95% CI, -0.18 to -0.02] percentage points) as did hospitalization for heart failure (rVE, 19.5% [95% CI, 3.3% to 33.1%]; absolute difference, -0.03 [95% CI, -0.06 to -0.01] percentage points). CONCLUSIONS AND RELEVANCE: This study found reduced incidence of cardiorespiratory hospitalization among those who received HD-IIV vs SD-IIV, driven by a lower incidence of CV hospitalizations, and particularly heart failure hospitalizations. These differences should be interpreted as exploratory findings in the setting of a large RCT with a neutral primary outcome. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05517174.

Aged↗