As I posted above, the IFR is probably higher than 0.6%, I trust nothing out of the CDC these days since it's obvious the scientists are being muzzled. For example, how could the CDC combine infection testing with antibody testing if it wasn't a political decision? No epidemiologist would make such a decision. The watering down of the CDC recommendations for safe opening was also political.
The Imperial College estimate was never taken seriously except by the media and a few 'so-called experts."
Anyone with a modicum of statistical and modeling experience could see through it in five minutes.
However, even if herd immunity is say 60%, infections don't stop when you hit herd immunity, the growth of infection slows until it peters out, somewhere in the 70-80% range. So 200M x the IFR of your choice is a quick and dirty back of the envelope guess.
The inaccuracy of the antibody tests suggests the estimates of total infections have been inflated. How much? Who knows. Right now the NYC study is probably the best data set (b/c a high degree of infection reduces the impact of inaccuracy/false positives in antibody tests). That suggests a 10:1 infected:confirmed ratio, which will decline as testing increases (i.e. you capture more infected people so there are fewer infected per confirmed case).