Early termination related to COVID pandemic

The purpose of this pilot study is to investigate and compare the effect of a mild inflammatory stimulus (typhoid vaccine) on immune response, mood and cognition in healthy volunteers compared to patients with history Major Depressive Disorder (MDD) (not currently depressed and no symptoms of depression in the past 6 months).

Study design: In this double blind randomized crossover design, each participant will receive saline injection or typhoid vaccine injection at the first study visit, and will then receive the other injection at the second study visit. All participants will undergo study procedures (clinical and imaging) in two separate sessions after each injection given at least 7 days apart (within 10-14 days).

Baseline blood samples will be taken and vital signs will be measured. Participants will be asked to complete the mood questionnaires and computerized reward tasks. Then, injections of normal saline will be administered intramuscularly in the deltoid muscle. At 1.5h, 3h, 4h and 6h after the injection, the subjects will complete the mood questionnaires and vital signs will be assessed. The computer based task will be repeated at 3h.

Between3h and 6h after the injection blood samples will be collected for cytokines measurement. At 4h, a structural magnetic resonance imaging (MRI), and Functional magnetic resonance imaging (fMRI) will be done.

Follow up visits/calls with the patients will be set to check their physical and mood status.

Inclusion Criteria:

• Healthy volunteers, male or female; aged 18-65
• Subjects with history of Major depression (currently asymptomatic - symptom free for more than 6 months)
• Medication free, if not feasible being on antidepressants will be allowed

Exclusion Criteria:

• Volunteers who received this vaccine within 3 years or any other vaccine within 3 months
• Patients with existing inflammatory conditions (connective tissue disorder, autoimmune conditions, neoplastic disease, chronic infections, etc.)
• Patients with acute viral or bacterial infection
• Hospitalized patients
• Patients in acute phase of illness
• Current active medical condition that affect brain anatomy, neurochemistry, or function, e.g. liver insufficiency, kidney insufficiency, cardiovascular problems, systemic infections, cancer, hypothyroidism, auto-immune diseases, and any brain disorder (seizure disorder, stroke, dementia, degenerative neurologic diseases)
• History of any brain diseases, including seizures, stroke, meningitis, encephalitis, dementia, degenerative brain diseases, and serious head injury with loss of consciousness
• Family history of hereditary neurologic disorder
• Floating metallic objects in the body
• Pregnancy
• Exposure to regular use of anti-inflammatory drugs in the last one month
• Excessive exercise, consumption of caffeinated beverages or alcohol, high-fat meals 12 hours before testing
• History of tobacco, alcohol, or drug abuse or dependence.
• History of allergic reaction to vaccination or serious allergic reaction to shellfish or egg allergy

The study clinician/ nurse will be aware of the nature of the injection. The study subjects and researcher collecting/analyzing the data will remain blinded to the intervention due to the possible confounding effects of the participant expectations and researcher analyzing the data.