Background: \- Influenza is a common viral infection, but it can be deadly for some people. Researchers want to learn more about how the body fights this virus. They want to study this in people who have recently been infected with influenza. They hope this can help them create more effective influenza vaccines. Objective: \- To learn about long-term changes in the body s immune system after influenza infection. Eligibility: \- People who have completed a previous LID Clinical Studies Unit influenza challenge study or current or prior participation in an LID natural history study and are willing to have samples stored for future research. Design: * Eligible participants will be asked to visit the clinic every 3 months for 2 years. * During each visit, participants will have blood drawn from an arm vein using a needle and a syringe and a nasal sample. * Participants will have a medical history and physical exam and vital signs performed. This will include blood pressure, heart rate, breathing rate, temperature, weight, and finger-measured blood oxygen. They will answer questions about any medicines taken and possible recent illnesses. * If participants have symptoms of influenza, they may have an additional sample taken from the nose. * Participants will complete a health questionnaire once a month on a secure website. Participants may also give their responses over the telephone.
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To characterize the timing of peak antibody response to hemagglutinin (HA) and neuraminidase (NA) post influenza challenge or after natural infection To evaluate the long-term variability of hemagglutinin inhibition (HAI) and neuraminidase inhib...
Timeframe: 2 years