TY - JOUR
T1 - High-Dose vs Standard-Dose Influenza Vaccine and Cardiovascular Outcomes in Older Adults
T2 - A Prespecified Secondary Analysis of the DANFLU-2 Randomized Clinical Trial
AU - Johansen, Niklas Dyrby
AU - Modin, Daniel
AU - Loiacono, Matthew M.
AU - Harris, Rebecca C.
AU - Dufournet, Marine
AU - Larsen, Carsten Schade
AU - Larsen, Lykke
AU - Wiese, Lothar
AU - Dalager-Pedersen, Michael
AU - Claggett, Brian L
AU - Janstrup, Kira Hyldekær
AU - Bartholdy, Katja Vu
AU - Bernholm, Katrine Feldballe
AU - Borchsenius, Julie Inge-Marie Helene
AU - Davidovski, Filip Soeskov
AU - Davodian, Lise Witten
AU - Dons, Maria
AU - Duus, Lisa Steen
AU - Espersen, Caroline
AU - Fussing, Frederik Holme
AU - Jensen, Anne Marie Reimer
AU - Landler, Nino Emanuel
AU - Langhoff, Adam Cadovius Femerling
AU - Lassen, Mats Christian Højbjerg
AU - Nielsen, Anne Bjerg
AU - Ottosen, Camilla Ikast
AU - Sengeløv, Morten
AU - Skaarup, Kristoffer Grundtvig
AU - Pareek, Manan
AU - Solomon, Scott D.
AU - Landray, Martin J.
AU - Gislason, Gunnar H.
AU - Køber, Lars
AU - Sivapalan, Pradeesh
AU - Martel, Cyril Jean-Marie
AU - Jensen, Jens Ulrik Stæhr
AU - Biering-Sørensen, Tor
PY - 2025/11/1
Y1 - 2025/11/1
N2 - 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.
AB - 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.
KW - Humans
KW - Influenza Vaccines/administration & dosage
KW - Aged
KW - Male
KW - Female
KW - Influenza, Human/prevention & control
KW - Cardiovascular Diseases/epidemiology
KW - Denmark/epidemiology
KW - Aged, 80 and over
KW - Hospitalization/statistics & numerical data
KW - Vaccine Efficacy
KW - Vaccines, Inactivated/administration & dosage
UR - https://www.scopus.com/pages/publications/105021467983
U2 - 10.1001/jamacardio.2025.3460
DO - 10.1001/jamacardio.2025.3460
M3 - Journal article
C2 - 40884442
SN - 2380-6583
VL - 10
SP - 1186
EP - 1194
JO - JAMA Cardiology
JF - JAMA Cardiology
IS - 11
ER -