The only thing experts can say for sure about this flu season is that it won't be similar to any other. There will be multiple flu viruses circulating, one of which most people are defenseless against. "This year we are in uncharted territory," says Centers for Disease Control and Prevention director Thomas Frieden. "What will happen in the coming weeks and months will only become clear in the weeks and months ahead." Here is a handy guide to prepare for flu season by USA TODAY's Steve Sternberg, compiled from information provided by the CDC and other sources.