Background.  Healthy volunteer wild-type influenza challenge models offer a unique opportunity to evaluate multiple aspects of this important virus. Such studies have not been performed in the United States in more than a decade, limiting our capability to investigate this virus and develop countermeasures. We have completed the first ever wild-type influenza A challenge study under an Investigational New Drug application (IND). This dose-finding study will lead to further development of this model both for A(H1N1)pdm09 and other strains of influenza.

Methods.  Volunteers were admitted to an isolation unit at the National Institutes of Health Clinical Center for a minimum of 9 days. A reverse genetics, cell-based, Good Manufacturing Practice (GMP)–produced, wild-type A(H1N1)pdm09 virus was administered intranasally. Escalating doses were given until a dose was reached that produced disease in a minimum of 60% of volunteers.

Results.  An optimal dose of 10⁷ tissue culture infectious dose 50 was reached that caused mild to moderate influenza disease in 69% of individuals with mean viral shedding for 4–5 days and significant rises in convalescent influenza antibody titers. Viral shedding preceded symptoms by 12–24 hours and terminated 2–3 days prior to symptom resolution, indicating that individuals may be infectious before symptom development. As expected, nasal congestion and rhinorrhea were most common, but interestingly, fever was observed in only 10% of individuals.

Conclusions.  This study represents the first healthy volunteer influenza challenge model using a GMP-produced wild-type virus under an IND. This unique clinical research program will facilitate future studies of influenza pathogenesis, animal model validation, and the rapid, efficient, and cost-effective evaluation of efficacy of novel vaccines and therapeutics.

Clinical Trials Registration.  NCT01646138.