Nationwide Utilization of Danish Government Electronic Letter System for Confirming the Effectiveness of Behavioral Nudges in Increasing InFLUenza Vaccine Uptake Among Older Adults (NUDGE-FLU-2)

Nationwide Utilization of Danish Government Electronic Letter System for Confirming the Effectiveness of Behavioral Nudges in Increasing InFLUenza Vaccine Uptake Among Older Adults

Nationwide Utilization of Danish Government Electronic Letter System for Confirming the Effectiveness of Behavioral Nudges in Increasing InFLUenza Vaccine Uptake Among Older Adults

In randomized clinical trials and observational studies, influenza vaccination has been shown to be effective in reducing influenza-related illness, hospitalizations, cardiovascular events, and mortality in select populations. However, the real-world effectiveness of influenza vaccination is limited by its uptake. Conducted during the 2022/2023 influenza season, the first NUDGE-FLU trial demonstrated the effectiveness of two electronic behavioral nudging letter strategies in increasing influenza vaccination rates among older adults in Denmark - a letter highlighting potential cardiovascular benefits of vaccination and a standard informational letter sent at baseline and repeated at day 14. This present study will once again investigate whether digital behavioral nudges delivered via the official, mandatory Danish electronic letter system can increase influenza vaccine uptake among older adults including whether the effectiveness of previously successful strategies can be confirmed during a subsequent influenza season.

The study is a prospective, randomized, open-label implementation trial. The study population will consist of persons aged >=65 years at January 15, 2024 - this age group is eligible for free-of-charge influenza vaccination in the official Danish vaccination program. Subjects will be identified through Danish nationwide health registries including the Danish Civil Registration System. Individuals will be randomized to 1 of 7 arms (1 usual care arm and 6 intervention arms) with each testing different nudging strategies employing various behavioural economic principles. The interventions will be delivered through the official, mandatory Danish electronic letter system. All subject data will be retrieved from the Danish nationwide registries with the exception of information on intervention allocation. Endpoints will be retrieved at prespecified dates using prespecified search algorithms.

This group will receive a standard letter on the benefits of influenza vaccination without behavioral economic enhancement

Text added to the standard letter highlighting potential cardiovascular benefits of influenza vaccination

Text added to the standard letter highlighting potential respiratory disease-related benefits of influenza vaccination

Text added to the standard letter highlighting potential risks of not receiving influenza vaccination

The control arm will receive no letter to reflect the background vaccination uptake. Intervention arms will test the effects of different letters developed using behavioral economic principles.

Total number of heart failure events (incident heart failure and first and recurrent heart failure hospitalizations)

Number of participants who filled a prescription for any guideline-directed medical therapy for heart failure

Number of participants who filled a prescription for a sodium-glucose cotransporter 2 inhibitor or glucagon-like peptide 1 receptor agonist

Inclusion Criteria: Age >=65 years at January 15, 2024 (eligible for free-of-charge influenza vaccination in the Danish public health system) Access to the official, mandatory Danish electronic mailbox system Exclusion Criteria: Persons living in nursing homes (approximated as any person living at an address with >=6 inhabitants aged 80 years and above) Known to have already scheduled influenza vaccination appointment

Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte

Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte

Data will be collected from Danish administrative health registries, which are subject to Danish legislation and can only be made available to a third party under certain conditions. Please contact the sponsor-investigator in case of any inquiries.