Long-term Observation of Hemagglutinin and Neuraminidase Inhibition Antibody Titers After Influenza Challenge

Post Influenza

Natural History, Longitudinal Observation, Influenza Like Infection (ILI), Immunity, Flu

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....

Circulating anti-influenza antibodies are an important factor in predicting clinical illness and severity in those infected with influenza. Specific antibodies against influenza include proteins targeting hemagglutinin (HA) and neuraminidase (NA). Lifelong immunity does not occur with influenza, either from natural infection or from vaccination. Due to the antigenic variation of Influenza A, individuals may become infected multiple times with the same subtype of influenza and even with the same strain. In the setting of natural infection and vaccination, antibody titer levels can persist initially, but then wane over time. In our previous challenge studies, measurements of antibody responses have been focused solely on the acute infection period up to 2 months after initial infection. Long-term changes in immunity have not been investigated. The challenge setting gives us the unique ability to follow individuals from a specific, known and well-characterized exposure/illness to measure long-term changes in antibody titers from a pre-exposure baseline. This study could offer unique insight into how anti-influenza antibody titers change over time naturally and in response to other infections and life events. This type of controlled study has never been done and we believe monitoring titers long-term will help us better understand protective correlates of influenza. In this natural history study, we will follow individuals who have undergone influenza challenge or have been naturally infected with influenza to evaluate changes in anti-influenza antibody titers over a 2-year period. Subjects will be followed for symptoms of influenza-like illness (ILI) and other changes in clinical status through quarterly clinical evaluations with blood draws. Monthly questionnaires will be used to follow subjects in between visits.

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