The influenza virus can kill tens of thousands of Americans in any given year. And this year’s flu season looks like it could be a doozy. Infection rates are higher than they were at this time in recent years, and the strain that hit the southern hemisphere caused record hospitalizations and deaths in Australia. One problem: although the virus strain that scientists selected for the vaccine was the correct one, it mutated once it was put into eggs. Researchers say this kind of situation