Abstract Purpose The DANFLU-1 trial suggested lower incidence of hospitalizations for pneumonia and influenza, respiratory disease and all-cause mortality among older adults receiving high-dose (HD-IV) versus standard-dose (SD-IV) influenza vaccine. This study assessed the relative effectiveness of HD-IV versus SD-IV according to comorbidity in elderly individuals. Methods This was a post-hoc analysis of the DANFLU-1 randomized controlled feasibility trial of HD-IV versus SD-IV conducted during the 2021–2022 influenza season in adults aged 65–79 years. Outcomes assessed included influenza-related, respiratory, and cardiovascular hospitalizations, and mortality. We tested for effect modification by level of the Charlson Comorbidity Index (CCI) using ICD-10 codes up to 10 years prior to randomization. Results Of the 12,477 randomly assigned participants (mean age 71.7 ± 3.9 years, 47.1% female), 8,020 (64.3%) had CCI = 0, 3,560 (28.5%) had CCI = 1–2 and 893 (7.2%) had CCI ≥ 3. When comparing HD-IV with SD-IV, hazard ratios of hospitalizations for pneumonia and influenza were similar across CCI groups (HR 95%CI: 0.15 0.03–0.68 for CCI = 0, 0.36 0.11–1.15 for CCI = 1–2, 1.00 0.25-4.00 for CCI ≥ 3). Comparable patterns were found for hospitalizations for respiratory disease (0.46 0.17–1.20 for CCI = 0, 0.67 0.32–1.39 for CCI = 1–2, 0.66 0.24–1.87 for CCI ≥ 3) and all-cause mortality (0.28 0.09–0.86 for CCI = 0, 0.70 0.30–1.63 for CCI = 1–2, 0.57 0.24–1.36 for CCI ≥ 3). There was no statistical evidence of effect modification by CCI for any outcome. Conclusions The lower incidences of clinical outcomes for HD-IV compared to SD-IV were not significantly modified by CCI. The potential benefit of HD-IV versus SD-IV may therefore be applicable regardless of comorbidity burden. Further research is required to confirm these findings.
Bernholm et al. (Thu,) studied this question.
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