Fluad vs. Fluzone High-Dose Vaccine Effectiveness Among Adults ≥65 Years

August 3, 2026 updated by: Kaiser Permanente

Relative Vaccine Effectiveness of Adjuvanted Inactivated Influenza Vaccine (aIIV) vs High-Dose Inactivated Influenza Vaccine (HD-IIV) for Prevention of Lab-Confirmed Influenza Among Adults ≥65 Years of Age in the United States

This study will evaluate the relative vaccine effectiveness of quadrivalent adjuvanted inactivated influenza vaccine (aIIV4) versus quadrivalent high-dose inactivated influenza vaccine (HD-IIV4) in preventing polymerase chain reaction (PCR)-confirmed influenza and influenza-related outcomes in adults ≥65 years of age during the 2023/24, 2024/25, and 2026/27 influenza seasons. The study is an observational study conducted at Kaiser Permanente Northern California (KPNC), an integrated health care system in the United States.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Observational

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
1500000

Contacts and Locations

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

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Locations

  • United States
    • California
      • Oakland, California, United States, 94612
        • Recruiting
        • Kaiser Permanente Northern California (entire region)
        • Principal Investigator:
          • Nicola P. Klein, MD, PhD
        • Contact:

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

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Older Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

This study includes KPNC adults ≥65 years who receive Fluad or Fluzone High-Dose influenza vaccine as part of routine clinical care during the 2023/24, 2024/25, and/or 2026/27 influenza seasons.

Description

Inclusion Criteria:

  • Age ≥65 years at the time of influenza vaccination
  • KPNC member at the time of vaccination
  • Receive either aIIV4 or HD-IIV4 at a KPNC facility during the 2023/24 and/or 2024/25 influenza seasons

Exclusion Criteria:

  • Age <65 years at the time of influenza vaccination
  • Received either aIIV4 or HD-IIV4 in the inpatient setting
  • Receive more than one influenza vaccination during a single season period (i.e., 2023/24 or 2024/25 influenza seasons)
  • Receive an influenza vaccination outside of KPNC

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

Cohorts and Interventions

Group / Cohort

Group / Cohort

A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Fluad Recipients
Kaiser Permanente Northern California members aged ≥65 years who receive Adjuvanted Quadrivalent Inactivated Influenza Vaccine (aIIV4)
Biological: Adjuvanted Quadrivalent Inactivated Influenza Vaccine (aIIV4)
Fluad Quadrivalent vaccine is an inactivated influenza vaccine formulated to contain 60 mcg of hemagglutinin (HA) total, with 15 mcg from each of the four recommended influenza strains and the MF59 adjuvant in single-dose prefilled 0.5 mL syringes. Kaiser Permanente Northern California members ≥65 years may receive Fluad as part of routine clinical care during the influenza season.
Other Names:
  • Fluad
Fluzone High-Dose Recipients
Kaiser Permanente Northern California members aged ≥65 years who receive High-Dose Quadrivalent Inactivated Influenza Vaccine (HD-IIV4)
Biological: High-Dose Quadrivalent Inactivated Influenza Vaccine (HD-IIV4)
Fluzone High-Dose Quadrivalent vaccine is an inactivated split virion influenza vaccine formulated to contain 240 mcg of HA total, with 60 mcg from each of the four recommended influenza strains in single-dose prefilled 0.7 mL syringes. Kaiser Permanente Northern California members ≥65 years may receive Fluzone High-Dose as part of routine clinical care during the influenza season.
Other Names:
  • Fluzone High-Dose

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
PCR-confirmed influenza
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years who receive Fluad or Fluzone High-Dose will be retrospectively assessed for the presence of PCR-confirmed influenza. This outcome will be assessed in single-season analyses (2023/24, 2024/25, and 2026/27 separately) and a pooled analysis across all seasons.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Emergency department visit or hospitalization for PCR-confirmed influenza
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years who receive Fluad or Fluzone High-Dose will be retrospectively assessed for an emergency department visit or hospitalization for PCR-confirmed influenza. This outcome will be assessed in single-season analyses (2023/24, 2024/25, and 2026/27 separately) and a pooled analysis across all seasons combined.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
Hospitalization for PCR-confirmed influenza
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years who receive Fluad or Fluzone High-Dose will be retrospectively assessed for hospitalization for PCR-confirmed influenza. This outcome will be assessed in a pooled analysis across all seasons combined.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
Hospitalization for all-cause community-acquired pneumonia
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years who receive Fluad or Fluzone High-Dose will be retrospectively assessed for hospitalization for all-cause community-acquired pneumonia. This outcome will be assessed in single-season analyses (2023/24, 2024/25, and 2026/27 separately) and a pooled analysis across all seasons combined.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Hospitalization for cardiovascular events
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years who receive Fluad or Fluzone High-Dose will be retrospectively assessed for hospitalization for cardiovascular events. This outcome will be assessed in single-season analyses (2023/24, 2024/25, and 2026/27 separately) and a pooled analysis across all seasons combined.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
PCR-confirmed influenza in subgroups with comorbidities
Time Frame: ≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)
KPNC members ≥65 years with comorbidities (e.g., cardiovascular and respiratory conditions, diabetes, obesity) who receive Fluad or Fluzone High-Dose will be retrospectively assessed for hospitalization for PCR-confirmed influenza. This outcome will be assessed in a pooled analysis across all seasons combined.
≥14 days after vaccination until date of outcome, death, loss-to-follow-up, or end of each season (estimated May 2024, May 2025, or May 2027)

Collaborators and Investigators

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

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Kaiser Permanente

Collaborators

Collaborators

An organization other than the sponsor that provides support for a clinical study. This support may include activities related to funding, design, implementation, data analysis, or reporting.
Seqirus

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

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)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
August 17, 2023

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
May 1, 2027

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
May 1, 2028

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
August 28, 2023

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
September 1, 2023

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
September 8, 2023

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
August 5, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
August 3, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
July 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 2033496

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

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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