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

NCT ID NCT05517174

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

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.

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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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