The infection and hospitalization numbers at present do not indicate that herd immunity has kicked in yet.
If the herd has 50% immunity the R0 of the disease is halved. I suppose. With social distancing and prophylactic measures, the R0 can be reduced further. We need to get it well below 1, as close to 0 as possible.
A R0 of .8, for example, means that 500,000 infected infect 400,000 who infect 320,000 in turn and those infect 256,000 and so on.
Since it takes so long to recover you still have the risk of HCS overload.