The study is a pragmatic, registry-based, open-label, active-controlled, individually randomized trial. The Danish nationwide administrative health registries will be used for data collection including baseline information, follow-up data, and safety monitoring. The study aims to randomize up to approximately 208,000 participants over 2 influenza seasons with approx. 104,000 participants per season. In each season, participants will be individually randomized 1:1 to receive either QIV-HD or QIV-SD.
The purpose of this pragmatic randomized trial is to evaluate the relative vaccine effectiveness of high-dose quadrivalent influenza vaccine (QIV-HD) vs. standard-dose quadrivalent influenza vaccine (QIV-SD) in older adults. Participants will be randomized 1:1 to either QIV-HD or QIV-SD.