Muse
Lifer
I first encountered a decent explanation of herd immunity with respect to covid-19 in this Wired Magazine article, being interview of Dr. Larry Brilliant. It's from a while back but it's great. He was the chief consultant for Contagion and is quite expert.On the OP question, surely it will keep spreading till we achieve 'herd immunity', either via a vaccine or via unconstrained spread. If the latter, it's generally said that such immunity effect only kicks in at 60-70% infection level (sadly, I don't know of a clip of an actor of Oldman's caliber screaming '60 to 70 percent!').
But if something smart is done to suppress the spread (as South Korea has done?) then maybe it won't get to that point before we get a vaccine?
The Doctor Who Helped Defeat Smallpox Explains What's Coming
Epidemiologist Larry Brilliant, who warned of pandemic in 2006, says we can beat the novel coronavirus—but first, we need lots more testing.
That means, A, a large enough quantity of us have caught the disease and become immune. And B, we have a vaccine. The combination of A plus B is enough to create herd immunity, which is around 70 or 80 percent.