There's a lot of flu GOING around at the moment. to go around = to circulate

It's better not to look at 'around' by itself. 'going around' is a phrasal verb that can have several meanings. Here, 'the flu going around' means the flu is very active in the neighbourhood. That is, the flu is very common and it is being passed from person to person in the neighbourhood or region that is close to the speaker.

Thanks, Elle, for claryfing that.

In reference to the comment before mine, you can say "there's a lot of (the) flu going around" :) It is colloquial and kind of like "slang", but it is permissible.

Thanks, Courtney. That really helped. If you need some help with Spanish, just let me know.