Fluad vs. Fluzone High-Dose Vaccine Effectiveness Among Adults ≥65 Years
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ClinicalTrials.gov Identifier: NCT06029933 |
Recruitment Status :
Recruiting
First Posted : September 8, 2023
Last Update Posted : September 8, 2023
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Condition or disease | Intervention/treatment |
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Influenza Community-acquired Pneumonia Cardiovascular Events | Biological: Adjuvanted Quadrivalent Inactivated Influenza Vaccine (aIIV4) Biological: High-Dose Quadrivalent Inactivated Influenza Vaccine (HD-IIV4) |
Study Type : | Observational |
Estimated Enrollment : | 960000 participants |
Observational Model: | Cohort |
Time Perspective: | Retrospective |
Official Title: | Relative Vaccine Effectiveness of Adjuvanted Quadrivalent Inactivated Influenza Vaccine vs High-Dose Quadrivalent Inactivated Influenza Vaccine Among Adults ≥65 Years for the 2023-24 and 2024-25 Seasons |
Actual Study Start Date : | August 17, 2023 |
Estimated Primary Completion Date : | May 2025 |
Estimated Study Completion Date : | May 2026 |

Group/Cohort | Intervention/treatment |
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Fluad Recipients
Kaiser Permanente Northern California members aged ≥65 years who receive Adjuvanted Quadrivalent Inactivated Influenza Vaccine (aIIV4)
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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 Name: Fluad |
Fluzone High-Dose Recipients
Kaiser Permanente Northern California members aged ≥65 years who receive High-Dose Quadrivalent Inactivated Influenza Vaccine (HD-IIV4)
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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 Name: Fluzone High-Dose |
- 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 or May 2025) ]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 and 2024/25 separately) and a pooled 2-seasons analysis (2023/24 and 2024/25 combined).
- 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 or May 2025) ]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 and 2024/25 separately) and a pooled 2-seasons analysis (2023/24 and 2024/25 combined).
- 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 or May 2025) ]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 2-seasons analysis (2023/24 and 2024/25 combined).
- 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 or May 2025) ]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 and 2024/25 separately) and a pooled 2-seasons analysis (2023/24 and 2024/25 combined).
- 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 or May 2025) ]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 and 2024/25 separately) and a pooled 2-seasons analysis (2023/24 and 2024/25 combined).
- 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 or May 2025) ]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 2-seasons analysis (2023/24 and 2024/25 combined).

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Ages Eligible for Study: | 65 Years and older (Older Adult) |
Sexes Eligible for Study: | All |
Accepts Healthy Volunteers: | Yes |
Sampling Method: | Non-Probability Sample |
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

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.
Please refer to this study by its ClinicalTrials.gov identifier (NCT number): NCT06029933
Contact: Amber H. Hyman, PhD, MPH | 510-267-7571 | Amber.Hyman@kp.org |
United States, California | |
Kaiser Permanente Northern California (entire region) | Recruiting |
Oakland, California, United States, 94612 | |
Contact: Amber H. Hyman, PhD, MPH 510-267-7517 Amber.Hyman@kp.org | |
Principal Investigator: Nicola P. Klein, MD, PhD |
Responsible Party: | Kaiser Permanente |
ClinicalTrials.gov Identifier: | NCT06029933 |
Other Study ID Numbers: |
2033496 |
First Posted: | September 8, 2023 Key Record Dates |
Last Update Posted: | September 8, 2023 |
Last Verified: | September 2023 |
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 |
Influenza, Human Respiratory Tract Infections Infections Orthomyxoviridae Infections RNA Virus Infections |
Virus Diseases Respiratory Tract Diseases Vaccines Immunologic Factors Physiological Effects of Drugs |