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

Study Overview
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Brief Summary
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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.

Detailed Description
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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.

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

Conditions
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Influenza, Behavior and Behavior Mechanisms

Intervention / Treatment
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* Behavioral: Behavioral Economic Principles


Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| No Intervention: Usual Care<br>No letter | |
| Experimental: Standard Letter<br>This group will receive a standard letter on the benefits of influenza vaccination without behavioral economic enhancement | Behavioral: Behavioral Economic Principles<br>* 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.<br>|
| Experimental: Repeated Letter<br>The standard letter sent out two times instead of once | Behavioral: Behavioral Economic Principles<br>* 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.<br>|
| Experimental: Cardiovascular Gain-Framing Letter<br>Text added to the standard letter highlighting potential cardiovascular benefits of influenza vaccination | Behavioral: Behavioral Economic Principles<br>* 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.<br>|
| Experimental: Respiratory Gain-Framing Letter<br>Text added to the standard letter highlighting potential respiratory disease-related benefits of influenza vaccination | Behavioral: Behavioral Economic Principles<br>* 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.<br>|
| Experimental: Implementation Intention Prompt Letter<br>Implementation intention prompt added to the standard letter | Behavioral: Behavioral Economic Principles<br>* 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.<br>|
| Experimental: Loss-Framing Letter<br>Text added to the standard letter highlighting potential risks of not receiving influenza vaccination | Behavioral: Behavioral Economic Principles<br>* 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.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of participants who received an influenza vaccine |  | Up to 3 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Time from intervention delivery to influenza vaccination |  | Up to 3 months | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Influenza, Vaccination, Nudging, Behavioral Science