Recent antibody tests in a Dutch bloodbank suggest that just 3% of the population have had it.
Herd immunity is just a theoretical concept. It's possible that a Covid infection grants no longterm immunity.
Given how little we know about Covid, a policy of creating herd immunity is extremely reckless.
If herd immunity works in humans, how come I am cursed with a semi-cold for almost the entire winter, every winter, and the odd dose of 'flu as well, though touching wood, no 'flu this year yet, probably due to global warming, which may be the first positive thing I have found to think about that? Other than that, my heating bills should recede a bit like my hair. Well, if they receded as much as my hair has I would be delighted.