Scientists probe immune system secrets behind vaccines that protect for decades

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Able to understand and give informed consent. * Age 18-50 years. * Participants agree not to take any live vaccines 30 days before or after (14 days for inactivated) vaccination. * Women of child bearing potential must agree to use effective birth control for the first 3 months of the study. A negative urine pregnancy test must be documented prior to vaccination and prior to tissue sampling procedures. Exclusion Criteria: * History of allergy or serious adverse reaction, including Guillain-Barré syndrome, to a vaccine or vaccine products. * History of a medical condition resulting in impaired immunity (such as HIV infection, cancer, particularly leukemia, lymphoma, use of immunosuppressive or antineoplastic drugs or X-ray treatment). Persons with previous skin cancers or cured non-lymphatic tumors are not excluded from the study. * History of Hepatitis B or Hepatitis C infection. * Chronic clinically significant medical problems that could affect the immune response, require medication that would affect the immune response, or have signs or symptoms that could be confused with reactions to vaccination, including (but not limited to): 1. Insulin dependent diabetes 2. Severe heart disease (including arrhythmias) 3. Severe lung disease 4. Severe liver disease 5. Severe kidney disease 6. Grade 4 hypertension (\*Grade 4 hypertension per CTCAE criteria is defined as life-threatening consequences (e.g., malignant hypertension, transient or permanent neurologic deficit)) * Thymus gland problems (such as myasthenia gravis, DiGeorge syndrome, thymoma) or removal of thymus gland or history of uncontrolled autoimmune disorder. * Pregnancy or breast feeding, or plans to become pregnant in the first 3 months of study participation. * Receipt of blood products or immune globulin product within the prior 3 months. * Active duty military. * History of excessive alcohol consumption, drug use, psychiatric conditions, social conditions or occupational conditions that in the opinion of the investigator would preclude compliance with the trial. Additional Exclusion Criteria for YF-17D Arm * History of previous yellow fever, West Nile, Dengue, St. Louis encephalitis, or Japanese encephalitis vaccination or infection. * Previous residence in a country where there is a risk of yellow fever virus (YFV) transmission * History of allergy to eggs, chicken, or gelatin. Additional Exclusion Criteria for QIV Arm * History of influenza infection within the same influenza season.