It seems to me that the concept of burnout or herd immunity is not an on-off, yes/no reality. Reaching burnout or herd immunity does not require that there are ZERO deaths from COVID19.
Michael Levitt, in his tweet (set out above) that makes a prediction for the USA of less than 170,000 deaths at the point that burnout is reached, defines burnout as that point in time when there are no longer "excess deaths" when calculating deaths from ALL causes. He does not say that there will be ZERO deaths from COVID19, just that the infection rate of the virus will no longer be capable of rising.
At this point in time, based on where we are with COVID19, nobody knows what the outcome will be. Michael Levitt does not know. He is making a projection from all of the data that is available to him, using his experience and knowledge to do so. But, he does not know. I hope he is right with his current projection, that the burnout is close to 20% infection of the population and that we are closing in on that number in the USA. That means that we can get back to "normal" sooner rather than later.
I truly appreciate the vigorous debate here on TA. You guys are amazing! Your abilities to gather the data and information and then to debate its meaning is extremely helpful. Thank you! Kudos also to the doctors and other health professionals that have taken the time to describe their experiences and impart their acquired knowledge. I also appreciate those, like me, who do not have any specialized knowledge or experience, who are just trying to follow this strange new world and gain some understanding that we might not otherwise be able to have.