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Massive study tests whether a stronger flu shot saves more seniors from hospitalization

NCT ID NCT06506812

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 25, 2026 · Last updated Jun 26, 2026 · Updated 1 time

Summary

This study combines data from two large trials in Denmark and Spain involving over 466,000 older adults. It compares the high-dose flu vaccine (Efluelda/Fluzone High-Dose) to the standard-dose flu shot to see which better prevents severe outcomes like hospitalization for flu or pneumonia. The goal is to get clearer answers by pooling data from different countries and seasons.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
High-dose quadrivalent influenza vaccine (Efluelda/Fluzone High-Dose Quadrivalent) vs. standard-dose quadrivalent influenza vaccine
What this could lead to
If high-dose vaccine proves more effective, it could become the preferred flu shot for older adults, reducing hospitalizations and deaths from flu.
What could go wrong
This is a pooled analysis of completed trials, not a new experiment. The results may not apply to all populations or flu seasons, and high-dose vaccine may cause more local reactions.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 4

Runs after approval, following long-term safety and how well the treatment works in everyday use.

Participants

466,320 people

The number who actually took part.

Started

May 2025

Finished

Aug 2025

Lead sponsor

Other sponsor

The registry's catch-all category, for sponsors it does not file as a company, a government agency, or a research network.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

65 years and older

Sex

Anyone

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Pragmatic trials conducted to estimate the relative vaccine effectiveness of high-dose influenza vaccine compared with standard-dose influenza vaccine using the DANFLU-2 protocol or a protocol developed based on the DANFLU-2 protocol Exclusion Criteria: * Low data quality * Influenza circulation threshold was not met in any of the study seasons * Severe under-enrollment in all seasons

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Conditions

The condition(s) this trial relates to.

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Contacts and locations

Locations

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

    Hellerup, Capital Region, 2900, Denmark

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