Live virus challenge studies have played an important role in defining the correlates of protection of influenza in the past, and we believe they can continue to do so in the future. Since the last time a wild-type influenza challenge has been performed to investigate correlates of protection over 20 years ago, many new scientific tools and a significant increase in knowledge of the immune system have developed. In this study we will enroll participants at different hemagglutinin inhibition titer levels and evaluate this as a correlate of protection to the 2009 H1N1 while exploring the other possible correlates of protection that may be identified. This study represents the first opportunity to examine the correlates of protection of influenza in a fully validated and described wild-type virus challenge model. We believe that studies like this are an ideal use of a wild-type influenza challenge study and can lead to intelligent universal vaccine design as well as a basis to begin evaluating novel vaccine strategies in wild-type challenge studies in the future.