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

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).

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Key information

Conditions

Influenza A Infections Influenza, Human Orthomyxoviridae Infections RNA Virus Infections Respiratory Tract Diseases Respiratory Tract Infections Virus Diseases

Age range

18 year–64 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 4

Primary location

La Jolla Institute for Immunology

La Jolla, California, 92037, United States

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

Influenza Fluzone vaccine

Biological

Fluzone vaccine administered in both May-June and in September-October for each participant.

Primary outcomes

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.
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.

Sponsors and collaborators

Lead sponsor

La Jolla Institute for Immunology

Other

Registry information

Important dates

Study start: 2024
Primary completion: 2025
Study completion: 2025
First posted: Aug 23, 2024
Registry last updated: Feb 12, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

Published trials that share one or more normalized conditions with this study.

Completed