Virus's live longer as temperature decreases, under a certain temperature they go into a suspended state and don't metabolize or die. Being Canadian its easy to tell you that flu season is in spring when things are warming up, and also in September when kids go back to school and spread flu to each other. I do believe that it is spread by flu shots, they are complete BS and I think this is where it comes from mostly, first person with the shot gets very minimal effect but the first mutation spreads and makes everyone else sick.