Why your annual flu shot might work differently each year

NCT ID NCT04576377

Completed Knowledge-focused Sponsor: The University of Hong Kong Source: ClinicalTrials.gov ↗

First seen Jun 25, 2026 · Last updated Jun 27, 2026 · Updated 1 time

Summary

This completed study in Hong Kong enrolled 977 adults aged 18-45 to understand how getting the flu vaccine year after year changes the body's immune response. Participants received either the Flublok vaccine or a saline placebo. Researchers measured antibody levels and looked for reasons why some vaccinated people still catch the flu. The goal is to improve future flu vaccination strategies.

What this could mean

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

Active substance: Flublok (recombinant quadrivalent influenza vaccine)
What this could lead to: If successful, this study could help predict who benefits most from annual flu shots and why some vaccinated people still get the flu.
What could go wrong: This is an observational knowledge-harvesting study, not a test of a new treatment. Results may not apply to older adults or other populations.

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.

influenza prevention target

As listed by the trial registrant

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

INFLUENZA, HUMAN

Contacts and locations

Locations

The University of Hong Kong

Hong Kong, 00000, Hong Kong

More trials for these conditions

Other studies related to the condition(s) this trial covers.