“How many previously had covid and recovered?”
Just in the last week, CDC updated its estimate, to run through May 2021, from the start of the epidemic. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/burden.html
They put it around 120 Million. In the two months since, new infections have sped way up, with the Delta wave. I’d guess something like 5-10 Million more (possibly even more).
Roughly speaking, they estimate about three unreported infections, for each one confirmed by test, but that probably varies from place to place, and at different times.
We don’t have any good way (and I doubt CDC does either), of telling how many of those who were previously exposed are also counted among those who were infected. So we can’t just add 120 Million infected to 165 million fully vaccinated to get 285 Million with strong immunity (which would be like 85% of the US population). But natural immunity is a major component of our herd immunity.
In the Spring, vaccination was outpacing infection better than 10 to 1. But since vaccinations slowed way down, and Delta is spreading rapidly, we may be approaching closer to parity as the Delta wave peaks. After Delta, I think there will be too much widespread immunity for any future variant to have much of a run.
Let’s hope you are right. I think you are. You are also correct there is no way to know how many people really have natural immunity - the only way would be to do large scale antibody testing and I think we would find it would vary fairly widely between regions. It is also difficult to talk about natural immunity as a strategy because while it is easy to vaccinate and track the number of vaccinations I don’t think anyone would advocate infecting the nonimmune with covid….