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

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.

NCT Number	NCT06029933
Lead Sponsor	Kaiser Permanente Collaborators: Seqirus
Conditions	Influenza, Community-acquired Pneumonia, Cardiovascular Events
Enrollment	1,500,000 participants
Start Date	2023-08-17
Primary Completion	2027-05 (estimated)
Study Completion	2028-05 (estimated)
Updated on ClinicalTrials.gov	2026-08-05