The latest I've read from the CDC (a week ago, based on data from the week before) is that for every confirmed case, there are about 10 unconfirmed cases. If so, we are now closing in on a 10% exposure rate here in the U.S.

I've also read recently that the R₀ (reproduction number) is now looking like 2.5 at a minimum. With hygiene and distancing, that can be brought down below 1.0, of course, but we're all getting tired of doing the right thing. Upshot: Long-term, the herd immunity threshold (HIT) may need to be adjusted more toward the 65 to 70% level.

Nothing magical happens at the HIT. But in that vicinity, the virus has a harder time spreading and outbreaks tend to sputter to a halt or, at least, go into a slow endemic smolder. So, we are about 15% of the way to HIT, which means about another half-million deaths due to COVID-19 over some interval of time, to be determined by social dynamics and medical progress on vaccines, if any.

Ed Boysun brought up treatments in TPP the other day, which is the most promising set of possibilities at present. Unfortunately, other posters turned it political and nothing was learned by them. We need to turn our focus from preventing all infection to making infections more survivable. There are several paths forward on this approach...but all we hear about is the vaccine.

We will reach HIT just in time for immunity to weaken in recovered patients. And, of course, the older population is constantly being replaced by children who have no immunity. And, we can expect the virus to continue to evolve into new strains, some of which will not be affected by the first vaccines. Over time, the virus should become more infectious, though less lethal. Improved treatment is of utmost importance.