Both the number of viruses in initial flu infection, and the virus type, affects the patient's outcome. Mice infected by high concentrations developed immunity, and generated immune cells in the lungs to fight other strains. Mice that were infected with a relatively low concentration of the virus developed weaker immunity against the strain that infected them, did not build up this crucial population of immune cells in the lungs, and showed only delayed immunity toward other flu strains. This discovery could pave the way for new prophylactic strategies to fight flu infections and provides a novel basis for vaccine design. Learn more by clicking on the image or headline.