If I'm wrong please tell me, but I'd say that the reason it's not widely spread amongst homeless people is that A) homeless people don't travel to other countries and don't usually fraternize with people who do and B) they aren't usually frequenting enclosed public spaces. And that's assuming that homeless people aren't getting affected; maybe they are.
And the fact that a nine-year-old's Instagram is being used for this...I mean, come on.