Age-Associated Differences in Germinal Center Responses to Influenza and Rabies Vaccination in Humans

This study is being done to better understand how the immune system responds to vaccination against influenza and rabies. Researchers want to study how immune responses develop and change over time in the blood and in the lymph nodes that drain the vaccination site, following vaccination with two vaccines licensed by the U.S. Food and Drug Administration (FDA): the seasonal trivalent influenza vaccine (TIV) and the rabies vaccine (RabAvert). By studying these samples, researchers hope to learn how the body produces high-quality, long-lasting antibody and memory immune responses after vaccination. The study will also compare immune responses in younger adults to immune responses in older adults, because prior research suggests that the immune system's ability to respond to vaccination weakens with age.

Inclusion Criteria: 1. Healthy participants 18 to 40 years of age or ≥65 years of age. 2. Able to understand and give informed consent. 3. Willing to receive RabAvert vaccine. 4. Willing to receive TIV (trivalent influenza vaccine). 5. In stable health, as determined by medical history and targeted physical exam related to this history. 6. Willing to give blood and optional lymph node FNA (fine needle aspiration) samples. Exclusion Criteria: 1. Has a history of severe local or systemic reactions to any vaccination. 2. Has a history of severe allergic reaction to any component of the rabies or influenza vaccines. 3. Has a history of prior rabies vaccination, receipt of rabies post-exposure prophylaxis or rabies immunoglobulin, or known or suspected prior exposure to rabies virus. 4. Has received any influenza vaccines ≤ 180 days prior to the day of injection (Day 1). 5. Has a current or previous diagnosis of immunocompromising condition to include human immunodeficiency virus, immune-mediated disease requiring immunosuppressive treatment, or other immunosuppressive condition. 6. Has received systemic immunosuppressants or immune-modifying drugs for \> 14 days in total within 6 months prior to Screening (for corticosteroids ≥ 10 mg/day of prednisone equivalent) or is anticipating the need for immunosuppressive treatment at any time during participation in the study. 7. Is acutely ill or febrile (temperature \>38.0 C \[100.4F\] less than 72 hours prior to or at the Day 1 visit. Participants who meet this criterion may be rescheduled. 8. Currently has symptomatic acute or unstable chronic disease requiring medical or surgical care, to include significant change in therapy or hospitalization, at the discretion of the investigator. 9. History of excessive alcohol consumption, drug abuse, psychiatric conditions, social conditions or occupational conditions that in the opinion of the investigator would preclude compliance with the study. 10. Has received any vaccine ≤ 28 days prior to the injection (Day 1) or plans to receive a vaccine within 28 days before or after the study injection. These participants may be rescheduled. 11. Pregnant women and nursing mothers or women who are planning to become pregnant for the study duration. 12. Have donated blood, blood products or bone marrow within 30 days before study vaccination, plan to donate blood at any time during the duration of participant study participation, or plan to donate blood within 30 days after the last blood draw. 13. Any condition in the opinion of the investigator that would interfere with the proper conduct of the trial. 14. Unwilling to use an effective method of contraception if you are of childbearing potential.