The herd immunity threshold (HIT) is calculated using the basic reproductive number (R0), which is the rate of spread. The formula is 1-1/R0. For the original pre-April variant (D614G), the R0 was 2.5. 1-1/2.5 = 0.6 or 60%. The April variant jumped that up a bit. The latest variants from the UK and South Africa are still being evaluated, but early estimates have their R0 value at somewhere between 4.3 and 5.7. So in the worst case, you've got 1-1/5.7 or 82%.
The problem with Fauci is he says a lot of nonsense and never met a TV camera he didn't want to blab into endlessly. He's a media hound. If you get any good info from him, only half of it's any good and you'll never get the whole story.
The whole story is that the herd immunity threshold is met via inoculation; not ONLY vaccination. All available evidence shows that those who've been infected and those who've been vaccinated all show strong immune response against all known variants. About 76 million people in the US have already been infected or currently are infected with SARS-CoV-2. So that's 23% right there. Another ~21 million (6%) have received at least one dose of the vaccine already. At current trend levels, a month from now, with current trend levels, we can expect a total inoculated population closer to 39%.
I would expect us to be at the herd immunity threshold by July. After which point, while there may be small isolated outbreaks, we should see a fairly quick decline in new cases right down to nearly zero.
There are 27 million known infections in the US. 76 million would mean that you are estimating almost 3 times the number of known infections to calculate total infections. I've heard people say that the total number of infections is about 8 times higher than known infections.
Why do you estimate 76 million?