Of course, out of the confirmed and/or suspected total case load in order to get the number of people walking around infected/recovered we'll have to reduce that number somewhat. Some passed away. Some may have left the US. Some unfortunate people are very susceptible and have caught it 2 or even 3 times. So the number of people walking around with some level of natural immunity will be somewhat less than the 147 million.
Then we have the 200 million or so vaccinated which should {snort} have some immunity. Obviously there will be some fairly significant overlap between the natural immunity group and the vaccinated group. Many got vaccinated after being sick (knowingly sick or not). Many got sick after being vaccinated.
But still, even if we knock out 20 million from the 147, and even if we go with as much as 50% overlap. That's 273 or so million out of 330 million or so. That's nearly 83%. You'd think for most nominally transmissible infections this should be about the herd immunity level. Unless of course the vaccines aren't really helping...
“Unless of course the vaccines aren’t really helping...”
It may be that the bulk of the people who have not yet had COVID (and a good chunk of those who have) might have to get their case - vaccinated or not.
If that is the situation, there would be a lot of fuel left for Omicron to flare through - about half the population.
It does seem that the vaccines reduce severity/hospitalization/death significantly, but not so much protection from infection or transmission of Delta or Omicron.