The science of flu season

Flu season is in winter. Okay, great. But why? (Consider this an open thread for all your favorite humidifier recommendations.)

Why has this flu season been so mild?

Short answer: We don't know. Despite its ubiquity, there's a lot scientists don't know about the influenza virus. Helen Branswell is a great medical reporter. In this piece for the Winnipeg Free Press she explains why the flu virus makes seemingly simple questions frustratingly difficult to answer.