Key result
High-dose flu vaccine shows no benefit over standard-dose for respiratory hospitalizations regardless of ASCVD.
Why the study?
Does high-dose inactivated influenza vaccine reduce hospitalization for influenza or pneumonia compared to standard-dose vaccine in adults ≥65 years with or without ASCVD?
RCT (n=332,438)
Open-label
1:1
Yes
Does high-dose inactivated influenza vaccine reduce hospitalization for influenza or pneumonia compared to standard-dose vaccine in adults ≥65 years with or without ASCVD?
Effect estimate: rVE 6.87% (without ASCVD) and 4.71% (with ASCVD) (95% CI -2.52 to 15.42 (without ASCVD) and -11.58 to 18.63 (with ASCVD))
p-value: Pinteraction = .80
High-dose influenza vaccination showed similar relative vaccine effectiveness against respiratory and cardiovascular outcomes compared to standard-dose vaccination in older adults, regardless of pre-existing ASCVD.
The aim was to evaluate and compare the relative vaccine effectiveness (rVE) of high-dose (HD-IIV) vs. standard-dose inactivated influenza vaccination (SD-IIV) on respiratory and cardiovascular outcomes in persons with or without pre-existing atherosclerotic cardiovascular disease (ASCVD). A prespecified exploratory analysis of a pragmatic, open-label, individually randomized trial conducted in Denmark during three influenza seasons. Adults ≥65 years were randomized 1:1 to HD-IIV or SD-IIV. Baseline and outcome data were collected through nationwide registries. The primary outcome was hospitalization for influenza or pneumonia. Major adverse cardiovascular events (MACE) was defined as a composite of cardiovascular death, hospitalization for myocardial infarction, or hospitalization for stroke. Heterogeneity in rVE among participants with vs. without ASCVD was assessed. The incidence of all outcomes was higher in participants with pre-existing ASCVD (n = 46 825) vs. those without (n = 285 613). rVE was consistent among participants with and without ASCVD (all Pinteraction ≥ .05). The rVE for the primary outcome was 6.87% [95% confidence interval (CI), -2.52 to 15.42] among individuals without ASCVD and 4.71% (95% CI, -11.58 to 18.63) in those with (Pinteraction = .80). For influenza hospitalizations, the rVE was 42.88% (95% CI, 22.07-58.44) vs. 45.73% (95% CI, 16.68-65.16) in those without vs. with ASCVD (Pinteraction = .84). For MACE, the rVE was 4.29% (95% CI, -6.50 to 14.00) in participants without, and 0.30% (95% CI, -17.56 to 15.44) in participants with, pre-existing ASCVD (Pinteraction = .68). Among individuals ≥65 years, the rVE of HD-IIV vs. SD-IIV against respiratory and cardiovascular outcomes was similar among those with vs. without pre-existing ASCVD.
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Pareek et al. (2025) conducted an RCT in Atherosclerotic cardiovascular disease (ASCVD) (n=332,438). High-dose inactivated influenza vaccine (HD-IIV) vs. Standard-dose inactivated influenza vaccination (SD-IIV) was evaluated on Hospitalization for influenza or pneumonia (rVE 6.87% (without ASCVD) and 4.71% (with ASCVD), 95% CI -2.52 to 15.42 (without ASCVD) and -11.58 to 18.63 (with ASCVD), p=Pinteraction = .80). High-dose vs standard-dose influenza vaccine showed similar relative vaccine effectiveness for influenza or pneumonia hospitalization in adults ≥65 years with (4.71%) and without (6.87%) ASCVD.
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