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

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.

• INCLUSION CRITERIA:

• Completion of participation in an LID Clinical Studies Unit influenza challenge study or current or prior participation in an LID natural history study.
• Willing to have samples stored for future research.

CO-ENROLLMENT GUIDELINES:

Participants may be co-enrolled in other research studies. This will be addressed on a case-by-case basis with the approval of the principal investigator (PI) or associate investigator.

If a participant enrolls in another influenza challenge study, the participant will be removed from this study. The participant can re-enroll in this study after completion of the influenza challenge study and will be followed for two years following completion of the most recent influenza challenge study.

Exclusion criteria

Any condition or event that, in the PI s opinion, may substantially increase the risk associated with study participation or compromise the study s scientific objectives. Conditions that exclude a subject are considered to be unlikely, but an example would include a newly diagnosed medical condition that may alter a participant s immune system and make it unsafe to obtain scheduled blood samples for research purposes.