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Massive flu vaccine trial: does a stronger shot protect seniors better?

NCT ID NCT05517174

Prevention Sponsor: Tor Biering-Sørensen Source: ClinicalTrials.gov ↗

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 Results may not be published yet.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This status has not been confirmed recently, so it may be out of date.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 large study tested whether a high-dose flu vaccine works better than the standard-dose shot in adults 65 and older. Over 332,000 participants were randomly assigned to receive either the high-dose or standard-dose vaccine. Researchers tracked hospitalizations for flu, pneumonia, and other serious illnesses to see which vaccine offered stronger protection.

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 (QIV-HD)
What this could lead to
If high-dose vaccine works better, it could become the standard flu shot for older adults, reducing hospitalizations and deaths from flu.
What could go wrong
The trial is large and completed, but results may show only a small benefit or none. High-dose vaccine can cause more local side effects like soreness.

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

332,438 people

The number who actually took part.

Started

Sep 2022

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

Accepted

You do not need to have the condition being studied to take part.

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: * Age 65 years and above (this inclusion criterion will be modified according to the Danish government's official recommendations for the 2022/2023 and 2023/2024 influenza seasons) * Informed consent form has been signed and dated Exclusion Criteria: * There are no specific exclusion criteria for this study

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Conditions

The condition(s) this trial relates to.

pneumonia influenza prevention target

As listed by the trial registrant

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

Influenza

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

  • Danske Lægers Vaccinations Service

    Søborg, 2860, Denmark

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