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

NCT06600490 | Completed

• 1 other identifier: NUDGE-FLU-CHRONIC-2
• Study Type: interventional
• Target: 308,978
• Locations: 1 country
• Sites: 1

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.

Conditions

Influenza; Behavior and Behavior Mechanisms

Keywords

Influenza; Vaccination; Nudging; Behavioral Science; Randomized Trial; Registry

Outcome Measures

Primary Outcomes (1)

• Number of participants who received an influenza vaccine

  Up to 3 months

Secondary Outcomes (1)

• Time from intervention delivery to influenza vaccination

  Up to 3 months

Other Outcomes (25)

• Number of participants with laboratory-confirmed influenza

  Up to 8 months

• Number of participants with a hospitalization for influenza or pneumonia

  Up to 8 months

• Number of participants with a hospitalization for any respiratory disease

  Up to 8 months

Study Arms (7)

Usual Care

NO INTERVENTION

No letter

Standard Letter

EXPERIMENTAL

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

Behavioral: Behavioral Economic Principles

Repeated Letter

EXPERIMENTAL

The standard letter sent out two times instead of once

Behavioral: Behavioral Economic Principles

Cardiovascular Gain-Framing Letter

EXPERIMENTAL

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

Behavioral: Behavioral Economic Principles

Repeated Cardiovascular Gain-Framing Letter

EXPERIMENTAL

The cardiovascular gain-framing letter sent out two times instead of once

Behavioral: Behavioral Economic Principles

Respiratory Gain-Framing Letter

EXPERIMENTAL

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

Behavioral: Behavioral Economic Principles

Implementation Intention Prompt Letter

EXPERIMENTAL

Implementation intention prompt added to the standard letter

Behavioral: Behavioral Economic Principles

Interventions

Behavioral Economic Principles BEHAVIORAL

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.

Cardiovascular Gain-Framing Letter; Implementation Intention Prompt Letter; Repeated Cardiovascular Gain-Framing Letter; Repeated Letter; Respiratory Gain-Framing Letter; Standard Letter

Eligibility Criteria

• Age: 18 Years - 64 Years
• Sex: all
• Healthy Volunteers: No
• Age Groups: Adult (18-64)

You may qualify if:

• 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

You may not qualify if:

• None

Sponsors & Collaborators

• Tor Biering-Sørensen: lead

Study Sites (1)

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

Hellerup, Capital Region, 2900, Denmark

Location

Related Publications (1)

• Johansen ND, Vaduganathan M, Bhatt AS, Modin D, Claggett BL, Janstrup KH, Larsen CS, Larsen L, Wiese L, Dalager-Pedersen M, Kober L, Solomon SD, Sivapalan P, Jensen JUS, Martel CJ, Krause TG, Biering-Sorensen T. Digital Nudges to Increase Influenza Vaccination in Patients with Chronic Diseases. NEJM Evid. 2026 Jan;5(1):EVIDoa2500265. doi: 10.1056/EVIDoa2500265. Epub 2025 Nov 10.

  PMID: 41213006 DERIVED

MeSH Terms

Conditions

Influenza, Human; Behavior

Condition Hierarchy (Ancestors)

Respiratory Tract Infections; Infections; Orthomyxoviridae Infections; RNA Virus Infections; Virus Diseases; Respiratory Tract Diseases

Study Officials

• Tor Biering-Sørensen, MD, MSc, MPH, PhD

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

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: OTHER
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Professor, MD, MSc, MPH, PhD

Study Record Dates

• First Submitted: September 13, 2024
• First Posted: September 19, 2024
• Study Start: October 1, 2024
• Primary Completion: January 1, 2025
• Study Completion: May 31, 2025
• Last Updated: September 12, 2025

Record last verified: 2025-09

Data Sharing

• IPD Sharing: Will share

Locations

DK (1)