Cellular and humoral immune responses in individuals with active influenza infection will be assessed. Each year, up to 50 participants will be enrolled. The investigators hypothesize that influenza infection will elicit mostly memory immune responses rather than de novo immune responses to infection.

Using samples collected from individuals after influenza virus vaccination, the investigators have shown that immune cells primed by previous influenza exposures are recruited to produce antibodies against newer viral strains. The investigators previous work indicate that the majority of the immune cells that respond to influenza vaccination are from the memory compartment, suggesting that 'immune imprinting' greatly affects the specificity of antibodies elicited by influenza vaccines. It remains less clear how prior influenza virus exposures impact immunity elicited by influenza virus infections. Compared to vaccinated individuals, it is more difficult to enroll influenza virus infected patients and track their immune responses over time. Viral antigens can persist for longer amounts of time following influenza virus infections relative to influenza vaccinations. It is therefore possible that influenza virus infections more efficiently prime de novo immune responses compared to influenza virus vaccinations. In this study, the investigators will longitudinally collect serum, PBMC, and respiratory samples from influenza virus-infected individuals from the University of Pennsylvania Health System characterize the cellular and humoral immune responses elicited by influenza virus infections.

Inclusion Criteria:

1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study procedures and availability for the duration of the study
3. Aged 18 years and older
4. Influenza positive test result performed within the University of Pennsylvania Health System

Exclusion Criteria:

1. Known latex allergy
2. Immunosuppression as a result of an underlying illness or treatment with immunosuppressive or cytotoxic drugs, or use of anticancer chemotherapy or radiation therapy within the preceding 36 months
3. Pregnancy due to the volume of blood collected in this study
4. Treatment with immunoglobulin or another blood product within the 3 months prior to enrollment in this study
5. Any neoplastic disease (excluding non-melanoma skin cancer or prostate cancer that is stable in the absence of therapy) or a history of any hematological malignancy ("active" is defined as having received treatment within the past 5 years)
6. Known acute or chronic medical condition that, in the opinion of the investigator or appropriate sub-investigator, would interfere with the evaluation of immune responses
7. Intends to donate blood during the study period
8. A known human immunodeficiency virus, hepatitis B, or hepatitis C infection
9. Any condition that would, in the opinion of the site investigator, place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol
10. Prolonged inpatient hospitalization that disrupts or interferes with study procedures.
11. Weigh less than 110lbs

Up to 50 influenza virus-infected participants who have tested positive for influenza virus infection within the University of Pennsylvania Health System will be enrolled in the study. Potential candidates will be in the Emergency Department with influenza-like symptoms and will be eligible once the eligibility criteria are met.

Protocol and statistical analysis plan may need to be shared for publication.

At publication

Per journal publication policy