Flu season is in full swing. It would have been on time if it showed up in November, or even in March - unlike the actual seasons, the timing of flu season is a little hard to predict. Except for one thing: it always happens in winter.
In fact, everywhere on Earth where people have a winter season, they also have a flu season. Here's an illustrated explanation of why the world's most obnoxious virus at least doesn't stick around all year.