As the number of deaths correlation to the pandemic H1N1 virus, usually known as "swine flu," continues to rise, scientists have been scrambling to decipher its inner workings and explain why the incidence is lower than expected in elderly adults. In a study available online and appearing in a future issue of Proceedings of the National Academy of Sciences, a UT Southwestern Medical Center researcher and his collaborators in California show that the molecular makeup of the current H1N1 flu strain is strikingly different from prior H1N1 strains as well as the normal seasonal flu, particularly in structural parts of the virus normally recognized by the immune system.