NCT06029933 · Kaiser Permanente
Fluad vs. Fluzone High-Dose Vaccine Effectiveness Among Adults ≥65 Years
What this study is about
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.
View original scientific description
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.
Interventions
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.
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.
Primary outcome measures
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.
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
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
Where
- Oakland, California
Collaborators
Seqirus
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Aug 5, 2026 · Source of record for eligibility and locations