Feasibility of Randomizing Danish Citizens Aged 65-79 Years to High-Dose Quadrivalent Influenza Vaccine vs. Standard-Dose Quadrivalent Influenza Vaccine in a Pragmatic Registry-Based Setting

Summary

The purpose of the study is to assess the feasibility of identifying, recruiting and randomizing a large sample of Danish citizens aged 65-79 years to high-dose quadrivalent influenza vaccine or standard-dose quadrivalent influenza vaccine in the 2021/2022 influenza season in a registry-based setting using Danish nationwide registries for all data collection including baseline information and outcome assessment.

Timeline

Start

2021-10-01

Primary completion

2022-05-31

Completion

2022-05-31

Publications

• Christensen J, Johansen ND, Bernholm KF, Borchsenius JIH, Janstrup KH, Modin D, Skaarup KG, Nealon J, Samson S, Loiacono M, Huang Y, Harris R, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Gislason GH, Kober L, Landray MJ, Sivapalan P, Jensen JUS, Biering-Sorensen T. Positive predictive value of respiratory infection diagnoses in the Danish National Patient Registry: A post hoc validation analysis of the DANFLU-1 trial. Int J Infect Dis. 2026 Jul;168:108703. doi: 10.1016/j.ijid.2026.108703. Epub 2026 Apr 13.
• Langhoff AF, Johansen ND, Modin D, Janstrup KH, Bartholdy KV, Espersen C, Nealon J, Samson S, Loiacono MM, Harris R, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Sivapalan P, Jensen JUS, Biering-Sorensen T. High-Dose vs. Standard-Dose Influenza Vaccine in Older Patients With Hypertension: A Post Hoc Analysis of DANFLU-1. J Clin Hypertens (Greenwich). 2025 Nov;27(11):e70177. doi: 10.1111/jch.70177.
• Duus LS, Johansen ND, Modin D, Janstrup KH, Nealon J, Samson S, Loiacono MM, Harris RC, Larsen CS, Reimer Jensen AM, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Sivapalan P, Staehr Jensen JU, Biering-Sorensen T. Effects of high-dose versus standard-dose influenza vaccine among patients with chronic lung disease: A prespecified analysis of the DANFLU-1 trial. Respir Investig. 2025 Nov;63(6):1309-1315. doi: 10.1016/j.resinv.2025.10.016. Epub 2025 Nov 1.
• Christensen J, Johansen ND, Janstrup KH, Modin D, Skaarup KG, Nealon J, Samson S, Loiacono M, Harris R, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Gislason GH, Kober L, Landray MJ, Sivapalan P, Jensen JUS, Biering-Sorensen T. Time of day for vaccination, outcomes, and relative effectiveness of high-dose vs. standard-dose quadrivalent influenza vaccine: A post hoc analysis of the DANFLU-1 randomized clinical trial. J Infect. 2024 Nov;89(5):106276. doi: 10.1016/j.jinf.2024.106276. Epub 2024 Sep 18.
• Christensen J, Johansen ND, Modin D, Janstrup KH, Nealon J, Samson S, Loiacono M, Harris R, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Gislason GH, Kober L, Landray MJ, Sivapalan P, Jensen JUS, Biering-Sorensen T. Relative Effectiveness of High-Dose Versus Standard-Dose Quadrivalent Influenza Vaccine in Older Adults With Cardiovascular Disease: A Prespecified Analysis of the DANFLU-1 Randomized Clinical Trial. Circ Cardiovasc Qual Outcomes. 2025 Feb;18(2):e011496. doi: 10.1161/CIRCOUTCOMES.124.011496. Epub 2024 Aug 31.
• Lassen MCH, Johansen ND, Modin D, Nealon J, Samson S, Dufournet M, Loiacono MM, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Jensen JUS, Sivapalan P, Vestergaard LS, Krause TG, Biering-Sorensen T. Effects of high-dose versus standard-dose quadrivalent influenza vaccine among patients with diabetes: A post-hoc analysis of the DANFLU-1 trial. Diabetes Obes Metab. 2024 May;26(5):1821-1829. doi: 10.1111/dom.15498.
• Johansen ND, Modin D, Nealon J, Samson S, Salamand C, Loiacono MM, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Jensen JUS, Sivapalan P, Vestergaard LS, Valentiner-Branth P, Krause TG, Biering-Sorensen T. A Pragmatic Randomized Feasibility Trial of Influenza Vaccines. NEJM Evid. 2023 Feb;2(2):EVIDoa2200206. doi: 10.1056/EVIDoa2200206. Epub 2023 Jan 23.
• Johansen ND, Modin D, Skaarup KG, Nealon J, Samson S, Dufournet M, Loiacono MM, Harris RC, Larsen CS, Jensen AMR, Landler NE, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Jensen JUS, Sivapalan P, Vestergaard LS, Valentiner-Branth P, Krause TG, Biering-Sorensen T. Effectiveness of high-dose versus standard-dose quadrivalent influenza vaccine against recurrent hospitalizations and mortality in relation to influenza circulation: A post-hoc analysis of the DANFLU-1 randomized clinical trial. Clin Microbiol Infect. 2024 Nov;30(11):1453-1459. doi: 10.1016/j.cmi.2024.01.017. Epub 2024 Jan 28.
• Johansen ND, Modin D, Nealon J, Samson S, Salamand C, Larsen CS, Claggett BL, Solomon SD, Landray MJ, Gislason GH, Kober L, Jensen JUS, Sivapalan P, Vestergaard LS, Valentiner-Branth P, Krause TG, Biering-Sorensen T. Feasibility of randomizing Danish citizens aged 65-79 years to high-dose quadrivalent influenza vaccine vs. standard-dose quadrivalent influenza vaccine in a pragmatic registry-based setting: rationale and design of the DANFLU-1 Trial. Pilot Feasibility Stud. 2022 Apr 21;8(1):87. doi: 10.1186/s40814-022-01044-w.

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