Well I don't really believe that it's because it hasn't been cold.

I live in Georgia, so the weather can get unseasonably warm at any time, and has been a lot this year. A cold front came in right before Christmas so it's in the 40's and 50's now. But before that the temperature was pretty warm for December even this far south.

I don't think that there are any more sick people here in the winter than there are in other places.