Male Speaker: We are hearing letters H and N, what do they mean? Michael Marcus: Influenza as a virus has different portions of the virus that help us identify the specific type of flu-virus that's hitting a community in any given year. The H and the N represent the most important identifying portions of the virus particle. Male Speaker: Are those genetic markers of sorts? Michael Marcus: They are genetic markers. The H and the N are carried in the genes of the influenza of virus and they are important because they are the portions of the virus that our immune system targets when we fight the virus, if we become --