Dr. Fauci OWNED Senator Paul. It was brilliant. Paul started up with some cockamamie theory of herd immunity despite there being lots of evidence to the contrary, and Fauci shut him down hard. Good.
There's no herd immunity in NYC or anywhere else as far as we can tell, with a few small exceptions in very tightly knit small communities. One very poor city in Brazil got slammed and may (just may, not confirmed) have had enough transmission to generate immunity.
There's pretty good data for NYC based on analysis of positivity rates (for active infections over time) plus growing serological testing (which detects anti-COVID-19 antibodies, showing past infection) that puts NYC around 22%... no where near what you need for herd immunity.
What's happened is this:
There was a LOT of infection injected into NYC early on: late February then in March due to NYC having a very high number of international travelers and being a port of call. And when the border shut down, huge numbers of people returned to the city.
Early on there wasn't much distancing / masking and the virus spread like wildfire through a city that was crammed full of people in close proximity on a routine basis.
They felt the pain, people got scared, they started distancing, and having lived through it, they took the measures to heart.
After the infection burned through those who were infected through March and early April, it slowed drastically and new cases fell rapidly; the death rate fell proportionately.
This same pattern has happened all over the place. It's not a surprise. If New Yorkers let down their guard, they will spike back up. But the strict precautions being taken in the city are holding it at bay.