An open-label, dose-ranging influenza challenge study in healthy adult volunteers to determine the optimal infection dose and safety of a recombinant H3N2 (A/Texas/ A/Texas/71/2017 (H3N2, clade 3C3a) influenza strain. The goal of this study is to find a challenge virus dose that is safe and can achieve a symptomatic influenza Attack Rate (AR) that will be sufficiently high for utilization in future vaccine or intervention studies. The optimal dose of the three considered is broadly defined as the minimum challenge virus dose that elicits the highest AR without meeting safety-stopping criteria. Additionally, viral recovery, clinical symptoms, and immune responses over the post-challenge period will be described by challenge dose group. This study will last for up to 1 year depending upon the number of challenge cohorts enrolled given the adaptive dose-escalation design. The populations are healthy males and non-pregnant, non-breastfeeding females aged = 18 and \< 46 years of age with a serum HAI antibody titer of \</=1:40 against influenza A/Texas/71/2017 (H3N2), clade 3C3a. The study will enroll and challenge up to 106 (plus 8 shams) healthy adult volunteers with the H3N2 (A/Texas/71/2017 (H3N2), clade 3C3a) influenza virus challenge strain. The primary objectives are: 1) To determine the optimal infectious dose of a recombinant influenza virus (A/Texas/71/2017 (H3N2), clade 3C3a) to be used as a clinical challenge strain in future vaccine efficacy or intervention studies as assessed by viral shedding and clinical symptoms. 2) To describe viral detection by quantitative and qualitative Reverse Transcription - Polymerase Chain Reaction (RT-PCR) from study subjects at baseline and post-challenge. 3) To document clinical symptoms from self-reported surveys and standardized symptom scales at baseline and post-challenge.
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Number and Percentage of Participants With Symptomatic Influenza Virus Infection After Challenge.
Timeframe: Day 2 through Day 8
Number and Percentage of Participants With Detected Viral Shedding in Nasopharyngeal (NP) Swabs Each Day Post-challenge.
Timeframe: Day 1 through discharge from the inpatient unit (Day 8 to Day 10)
Mean Peak Viral Load (VL) After Challenge
Timeframe: Day 2 through Day 8
Mean Duration of Viral Shedding
Timeframe: Day 2 through Day 8
Mean Maximum Cumulative Modified Jackson Score (MJS)
Timeframe: Day 2 through Day 8
Number and Percentage of Participants Symptomatic for Influenza.
Timeframe: Day 2 through Day 8