system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why/How is there a flu "season"?
gpt
Nobody is sure why, but it has to do with the weather and not the month.  
Australia has a different flu season than North America, for example.

It could be that people spend more time in  closed environments when it's cold, or it could be that the flu survives better in cold and dry weather.