Why does influenza spread primarily in the winter months?
It's because the virus is more stable and stays in the air longer when air is cold and dry.
"Influenza virus is more likely to be transmitted during winter on the way to the subway than in a warm room," said Peter Palese, a flu researcher who is professor and chairman of the microbiology department at Mount Sinai School of Medicine in New York and the lead author of the flu study
Intresting point...Flu season in northern latitudes is from November to March, the coldest months. In southern latitudes, it is from May until September. In the tropics, there is not much flu at all and no real flu season.
Read more here...http://www.iht.com/articles/2007/12/05/healthscience/05flu.php