InfluenzaNCT06600490
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
A study testing Behavioral Economic Principles in people with Influenza and Behavior and Behavior Mechanisms, run by Tor Biering-Sørensen at 1 site in Denmark.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 to 64 years
- Conditions the study is for
- Influenza, Behavior and Behavior Mechanisms
- What is being tested?
- Behavioral Economic Principles
- Type of treatment
- Vaccines, Lifestyle or therapy programme
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 308,978 participants
- Where
- 1 siteDenmark
- Study dates
- 1 Oct 2024to 31 May 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 64 years
- All sexes
- No healthy volunteers
- Adult
Who may be able to join
- 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
Show all 10Show fewer
- 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
Who cannot join
- None
Trial locations and contacts
1 site in 1 country.
Denmark1 site
Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte
Hellerup, Capital Region, 2900
About this study
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.
Read the 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.
- Conditions
- Influenza, Behavior and Behavior Mechanisms
- Being tested
- Behavioral Economic Principles
- Keywords
- Influenza, Vaccination, Nudging, Behavioral Science, Randomized Trial, Registry
- Medical subject headings
- Influenza, Human, Behavior
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Behavioral Economic PrinciplesBehavioural
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.
| Study group | Role | What they receive |
|---|---|---|
| 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 Receives: Behavioral: Behavioral Economic Principles |
| Repeated Letter | Experimental | The standard letter sent out two times instead of once Receives: Behavioral: Behavioral Economic Principles |
| Cardiovascular Gain-Framing Letter | Experimental | Text added to the standard letter highlighting potential cardiovascular benefits of influenza vaccination Receives: Behavioral: Behavioral Economic Principles |
| Repeated Cardiovascular Gain-Framing Letter | Experimental | The cardiovascular gain-framing letter sent out two times instead of once Receives: Behavioral: Behavioral Economic Principles |
| Respiratory Gain-Framing Letter | Experimental | Text added to the standard letter highlighting potential respiratory disease-related benefits of influenza vaccination Receives: Behavioral: Behavioral Economic Principles |
| Implementation Intention Prompt Letter | Experimental | Implementation intention prompt added to the standard letter Receives: Behavioral: Behavioral Economic Principles |
What is being measured
The primary outcome is the main question the study is designed to answer.
Number of participants who received an influenza vaccine
Measured: Up to 3 months
Secondary outcomes (1)
Time from intervention delivery to influenza vaccination
Measured: Up to 3 months
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted19 Sep 2024
- Study start1 Oct 2024
- Primary completion1 Jan 2025
- Study completion31 May 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for InfluenzaStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 308,978 participants (actual)
Sponsor and investigators
- Lead sponsor
- Tor Biering-Sørensen
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Tor Biering-Sørensen, Herlev and Gentofte Hospital
- Investigators
- Tor Biering-Sørensen, MD, MSc, MPH, PhD, Principal investigator, Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06600490
- Sponsor's protocol ID
- NUDGE-FLU-CHRONIC-2
- Status last verified
- Sep 2025
- First submitted
- 13 Sep 2024
- Last updated
- 12 Sep 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: 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.
Publications
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.
PubMed 41213006
Study at a glance
From the registry record, last updated by the sponsor on 12 Sep 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- 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
- ClinicalTrials.gov ID
- NCT06600490
- Acronym / sponsor ID
- NUDGE-FLU-CHRONIC-2
- Conditions
- Influenza, Behavior and Behavior Mechanisms
- Keywords
- Influenza, Vaccination, Nudging, Behavioral Science, Randomized Trial, Registry
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 308,978 participants (actual)
- Lead sponsor
- Tor Biering-SørensenUniversity, hospital or other
- Study start
- 1 Oct 2024 (actual)
- Primary completion
- 1 Jan 2025 (actual)
- Study completion
- 31 May 2025 (actual)
- First posted
- 19 Sep 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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 design
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 7
| Arm | Type | Receives |
|---|---|---|
| Usual Care | No intervention | –No letter |
| Standard Letter | Experimental | Behavioral: Behavioral Economic PrinciplesThis group will receive a standard letter on the benefits of influenza vaccination without behavioral economic enhancement |
| Repeated Letter | Experimental | Behavioral: Behavioral Economic PrinciplesThe standard letter sent out two times instead of once |
| Cardiovascular Gain-Framing Letter | Experimental | Behavioral: Behavioral Economic PrinciplesText added to the standard letter highlighting potential cardiovascular benefits of influenza vaccination |
| Repeated Cardiovascular Gain-Framing Letter | Experimental | Behavioral: Behavioral Economic PrinciplesThe cardiovascular gain-framing letter sent out two times instead of once |
| Respiratory Gain-Framing Letter | Experimental | Behavioral: Behavioral Economic PrinciplesText added to the standard letter highlighting potential respiratory disease-related benefits of influenza vaccination |
| Implementation Intention Prompt Letter | Experimental | Behavioral: Behavioral Economic PrinciplesImplementation intention prompt added to the standard letter |
Who may qualify
- Ages
- 18 to 64 years
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult
Key inclusion criteria (10 listed)
- 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:
- Access to the official, mandatory Danish electronic mailbox system
Key exclusion criteria (1 listed)
- None
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Behavioral Economic PrinciplesThe 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. | Behavioural | Cardiovascular Gain-Framing Letter, Implementation Intention Prompt Letter, Repeated Cardiovascular Gain-Framing Letter, Repeated Letter, Respiratory Gain-Framing Letter, Standard Letter |
Primary outcome
Number of participants who received an influenza vaccine
Time frame: Up to 3 months
1 secondary outcome
Time from intervention delivery to influenza vaccination
Time frame: Up to 3 months
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 12 Sep 2025.
- Derived from this study: PubMed 41213006Johansen 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.
- Individual participant dataSharing planned: Yes. 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.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Tor Biering-Sørensen, MD, MSc, MPH, PhD principal investigator
Center for Translational Cardiology and Pragmatic Randomized Trials, Department of Cardiology, Copenhagen University Hospital - Herlev and Gentofte
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Behavioral Economic Principles in people with Influenza and Behavior and Behavior Mechanisms, run by Tor Biering-Sørensen at 1 site in Denmark.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 10 inclusion and 1 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 12 Sep 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Denmark. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Number of participants who received an influenza vaccine (time frame: Up to 3 months). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT06600490, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 12 Sep 2025; AzTrials last refreshed its copy on 7 Nov 2026.