Recently, there was a big hope that in many locations so many people had already been infected with coronavirus that the entire population was close to herd immunity. This would have been nice if true.
Largely, however, as more testing for antibodies (which measures whether the subject has ever been infected) has become available, that hope hasn’t much panned out, outside of New York City and inner city Boston, where Ever Infected percentages seems to be in the lower double digits. Most other places — e.g., Spain with 5% ever infected — have been down in single digits. With the usual estimate of 60% infected needed for herd immunity under Let ‘er Rip conditions, that seems like a fairly long way to go in terms of hospitalizations and deaths.
For example, Swedish government officials back in April were trumpeting projections that by May 1, Stockholm would be perhaps halfway to Herd Immunity. But since then they’ve largely dummied up on the topic. I did find an Uppsala University press release from May 13:
Recently, tests were conducted on 454 individuals in Stockholm. These tests showed that only 7.5 per cent had antibodies, which differed significantly from the calculations made by experts at the Public Health Agency.
“We will wait to say more about how immunity is progressing until we have conducted another round of tests in late May.”
So recently, hope has been shifting toward the alternative idea that the herd immunity level needed isn’t, say, 60%, instead it’s much lower.
One way to test that would be to see what the highest percentage ever infected has been under Let ‘er Rip conditions, since the maximum seen in the wild would offer a lower bound. My recollection has been that percentages infected in various towns in Bergamo province have been over 50% … For example, back in early April, it was reported that in Castiglione D’Adda, 40 out of 60 blood donors had the antibodies.
But, all I’ve seen are Google Translates of Italian newspaper articles, which I don’t trust all that much. Has anybody seen a more reliable study of the highest infection rates found in the hardest hit places?