To compare the immunogenicity, cellular immune response, and safety between adjuvanted (aIIV4) and non-adjuvanted (IIV4) seasonal influenza vaccines in the Taiwanese elderly population with chronic medical conditions.
Adults aged 65 years or above
Presence of at least 1 chronic medical condition associated with increased risk of complicated influenza, including hypertension, chronic obstructive pulmonary disease (group A, B, E), asthma, congestive heart failure (ACC/AHA stage A, B, C, D), coronary arterial disease, diabetes mellitus, chronic liver disease (Child-Pugh score A, B, C) or chronic kidney disease (stage 1~4), neuromuscular disorders, hematological or solid organ malignancies, recipient of hematopoietic stem cell transplantation or solid organ transplantation.
Contraindications to influenza vaccination including history of severe adverse event after vaccination, such as anaphylaxis or Guillain-Barré Syndrome, or a severe bleeding tendency
Prior receipt of influenza vaccination during the current flu season.
Determination by the Principal Investigator (PI) that the participant is ineligible for enrollment based on clinical assessment.