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Can a blood test reveal why the flu shot fails some people?

NCT ID NCT03346772

Knowledge-focused Sponsor: University of Pennsylvania 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 Results may not be published yet.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This status has not been confirmed recently, so it may be out of date.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 Aug 27, 2026 · Last updated Aug 28, 2026 · Updated 1 time

Summary

Researchers at the University of Pennsylvania are studying how adults' immune systems respond to the seasonal flu vaccine. About 150 healthy adults will receive the standard flu shot, and researchers will draw blood at set times to measure antibody and lymphocyte responses. The goal is to understand why some people respond poorly to vaccination, which could help improve future flu vaccines.

What this could mean

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

Active substance
seasonal quadrivalent inactivated influenza vaccine
What this could lead to
If it works, this could help explain why some people mount weaker immune responses to the flu shot, pointing toward ways to improve vaccine effectiveness.
What could go wrong
This is an observational study of immune markers, not a test of a new vaccine. It may not reveal clear reasons for poor responses, and results may not apply to everyone.

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

150 people

The number who actually took part.

Started

Oct 2017

Finished

Jul 2026

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

18 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: * Community-dwelling adults able to provide consent who need influenza vaccination for standard of care Exclusion Criteria: * febrile illness at time of vaccination * active malignancy * use of immunosuppressing medications * blood donation in the past 60 days * influenza vaccinated during the preceding 6 months * allergic reactions to influenza vaccination

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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 vaccination

Contacts and locations

Locations

  • University of Pennsylvania

    Philadelphia, Pennsylvania, 19104, United States

More trials for these conditions

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