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

Not Applicable

Active, not recruiting

• Conditions: Influenza; Behavior and Behavior Mechanisms
• Interventions: Behavioral: Behavioral Economic Principles

• Registration Number: NCT06600490
• Lead Sponsor: Tor Biering-Sørensen

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. Conducted during the 2023/2024 influenza season, the first NUDGE-FLU-CHRONIC trial demonstrated the effectiveness of behavioral nudging letters in increasing influenza vaccination rates among adults aged 18-64 years with chronic diseases in Denmark. 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 adults aged 18-64 years with chronic diseases including whether the effectiveness of the previously successful strategies can be confirmed during a subsequent influenza season.

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.

Study Timeline

• Study First Submitted: 2024-09-13
• Study First Submitted QC: 2024-09-13
• Study First Posted: 2024-09-19
• Study Start: 2024-10-01
• Primary Completion: 2025-01-01
• Status Verified: 2025-02
• Last Update Submitted: 2025-02-05
• Last Update Posted: 2025-02-06
• Study Completion: 2025-05-31

Recruitment & Eligibility

• Status: ACTIVE_NOT_RECRUITING
• Sex: All
• Target Recruitment: 308978

Inclusion Criteria

1. Age 18-64 years

2. 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:

   1. Chronic lung disease
   2. Chronic cardiovascular disease other than hypertension
   3. Type 1 or type 2 diabetes mellitus
   4. Congenital or acquired immunodeficiency
   5. Impaired breathing due to muscular weakness
   6. Chronic renal or hepatic insufficiency
   7. Other chronic conditions with an increased risk of severe influenza as determined by the treating physician

3. Access to the official, mandatory Danish electronic mailbox system

Exclusion Criteria

None

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
Standard Letter	Behavioral Economic Principles	This group will receive a standard letter on the benefits of influenza vaccination without behavioral economic enhancement
Repeated Letter	Behavioral Economic Principles	The standard letter sent out two times instead of once
Cardiovascular Gain-Framing Letter	Behavioral Economic Principles	Text added to the standard letter highlighting potential cardiovascular benefits of influenza vaccination
Repeated Cardiovascular Gain-Framing Letter	Behavioral Economic Principles	The cardiovascular gain-framing letter sent out two times instead of once
Respiratory Gain-Framing Letter	Behavioral Economic Principles	Text added to the standard letter highlighting potential respiratory disease-related benefits of influenza vaccination
Implementation Intention Prompt Letter	Behavioral Economic Principles	Implementation intention prompt added to the standard letter

Primary Outcome Measures

Name	Time	Method
Number of participants who received an influenza vaccine	Up to 3 months

Secondary Outcome Measures

Name	Time	Method
Time from intervention delivery to influenza vaccination	Up to 3 months

Trial Locations

Locations (1)

Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte; 🇩🇰 Hellerup, Hovedstaden, Denmark