Characterization of Human Memory Immune Responses to Prior Yellow Fever Vaccination

The goal of this study is to characterize immune memory in humans who have previously received yellow fever vaccine. The project is designed to study the magnitude and persistence of both humoral, and cell-mediated immune memory generated post-vaccination. Since aging has an effect on the immune system (eg. decreased thymic output, replacement of hematopoietic cells in the bone marrow with adipocytes), the researchers will analyze the young adults (aged 18-45 years) and the older vaccinees (55 years or older) in separate groups.

The specific aims of the study are to:

• Determine the phenotypic and functional characterization of memory T cell responses to yellow fever vaccination
• Determine neutralizing antibody titer after yellow fever vaccination

Inclusion criteria

• Able to understand and give informed consent
• Age 18-45 years (Group 1) or 55 years and above (Group 2) at the time of yellow fever vaccination
• Documentation (international certificate of vaccination (yellow card) or medical record) indicating receipt of yellow fever vaccine.

Exclusion criteria

• Recipient of any vaccines within 30 days before the study visit (not applicable to older adults)
• History of a progressive and severe chronic medical condition resulting in impaired immunity (such as diabetes, kidney or liver dysfunction)
• Required use of immunosuppressive medications
• Reporting HIV, Hepatitis B (surface antigen positive) or Hepatitis C infections (antibody positive) on the medical/health history form
• Recipient of a blood product or immune globulin product within 42 days of study visit
• Reporting pregnancy