Characterizing Late-season Influenza Vaccine Responses to Compare the 2023 and 2024 Vaccine Formulations

February 10, 2026 updated by: Tal Einav, La Jolla Institute for Immunology
Every 1-2 years, the seasonal influenza vaccine composition changes to include updated viruses, yet the precise effects of updating the vaccine remain understudied. Since the vaccine formulation for each season (with a season defined as starting in July and ending the following June) expires on June 30, vaccine formulations cannot be compared head-to-head. Thus, the 2023 and 2024 vaccines have only been compared by analyzing people given the former vaccine in the fall of 2023 and people given the latter vaccine in the fall of 2024, and baseline repertoires may have greatly changed over the course of that year. To that end, the investigators will vaccinate a cohort with the 2023 influenza vaccine between May-June 2024, in order to compare responses between individuals receiving the 2023 vaccine last fall, the 2023 vaccine late in the season (this cohort), and the 2024 vaccine next fall. The investigators will further assess whether the late-season 2023 vaccine primed this cohort to respond better to the standard 2024 vaccine with standard timing (vaccine administered around September-October).

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Actual)

23

Phase

  • Phase 4

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • California
      • La Jolla, California, United States, 92037
        • La Jolla Institute for Immunology

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Be between 18-64 years of age
  • Males or non-pregnant, non-nursing females
  • Weigh at least 85 pounds for whole blood draw
  • Ability to provide signed informed consent
  • Subjects must plan to receive the intramuscular influenza vaccine at the La Jolla Institute for Immunology

Exclusion Criteria:

  • Received an influenza vaccine in the past year
  • Infection with human immunodeficiency virus, hepatitis B virus, or hepatitis C virus
  • History of certain anemias
  • Presence of significant cardiovascular disease, systemic diseases including, but not limited to, diabetes which is not controlled, renal disease, liver disease, malignancy, infection, or blood clotting disorder
  • Inability to provide informed consent
  • Recent whole blood donation within 56 days or leukapheresis within 112 days
  • Children (under 18 years of age), elderly (65 years of age or older), pregnant or nursing females
  • Individuals with egg allergies
  • Has ever had Guillain-Barré syndrome

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Late season influenza vaccine
Every participant receives the 2023 influenza vaccine between May-June 2024, and then the 2024 influenza vaccine in September-October 2024. Blood draws are taken at Day 0, 30, and 90 post-vaccination.
Biological: Influenza Fluzone vaccine
Fluzone vaccine administered in both May-June and in September-October for each participant.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Magnitude of Antibody Response After the Late-season 2023 Vaccine
Time Frame: 0, 30, and 90 days after the 2023 vaccine
The antibody response will be measured by hemagglutination inhibition (HAI) in adults between 18 and 64 years old who have not had an influenza vaccination prior to the study.
0, 30, and 90 days after the 2023 vaccine
Magnitude of the Antibody Response After the 2024 Vaccine
Time Frame: Day 0, 30, and 90 after the 2024 vaccine
The antibody response will be measured by hemagglutination inhibition (HAI) in adults between 18 and 64 years old who have not had an influenza vaccination prior to the study. This outcome was only performed on Arm 2.
Day 0, 30, and 90 after the 2024 vaccine

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

La Jolla Institute for Immunology

Investigators

  • Principal Investigator: Tal Einav, PhD, La Jolla Institute for Immunology

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

May 21, 2024

Primary Completion (Actual)

February 6, 2025

Study Completion (Actual)

February 6, 2025

Study Registration Dates

First Submitted

August 20, 2024

First Submitted That Met QC Criteria

August 21, 2024

First Posted (Actual)

August 23, 2024

Study Record Updates

Last Update Posted (Actual)

February 12, 2026

Last Update Submitted That Met QC Criteria

February 10, 2026

Last Verified

January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 286 (IRB Number of IGHCEAH)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

De-identified data will be included in all relevant publications.

IPD Sharing Time Frame

Data will be available upon publication.

IPD Sharing Access Criteria

Data will be available with no restrictions.

IPD Sharing Supporting Information Type

  • ANALYTIC_CODE

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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