Nationwide Utilization of Danish Government Electronic Letter System for Increasing InFLUenza Vaccine Uptake Among Adults With Chronic Disease

Study Overview
=================
Brief Summary
-----------------
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. This study will investigate whether digital behavioral nudges delivered via the official, mandatory Danish electronic letter system can increase influenza vaccine uptake among adults aged 18-64 years with chronic diseases.

Detailed Description
-----------------
The study is a prospective, randomized, open-label implementation trial. The study population will consist of persons aged 18-64 years identified as eligible for free-of-charge influenza vaccination due to a chronic condition. Subjects will be identified through Danish nationwide health registries using codes from the International Classification of Diseases, 10th revision (ICD-10). 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
-----------------
Nationwide Utilization of Danish Government Electronic Letter System for Increasing InFLUenza Vaccine Uptake Among Adults With Chronic Disease

Conditions
-----------------
Influenza, Behavior and Behavior Mechanisms

Intervention / Treatment
-----------------
* Behavioral: Behavioral Economic Principles


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria: Age 18-64 years Must be registered in the Danish nationwide registries as meeting at least one of the following eligibility criteria for free-of-charge influenza vaccination in the Danish public health system: Chronic lung disease Chronic cardiovascular disease other than hypertension Type 1 or type 2 diabetes mellitus Congenital or acquired immunodeficiency Impaired breathing due to muscular weakness Chronic renal or hepatic insufficiency Other chronic conditions with an increased risk of severe influenza as determined by the treating physician Access to the official, mandatory Danish electronic mailbox system Exclusion Criteria: None

Ages Eligible for Study
-----------------
Minimum Age: 18 Years
Maximum Age: 64 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
No

Study Plan
=================
How is the study designed?
-----------------

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?
-----------------
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
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Influenza, Vaccination, Nudging, Behavioral Science