We noted the recent antibody studies out of California. A study in Miami finds that 6% of the population has antibodies, while a study in New York found that 21% of people in New York City had antibodies, while 3.6% in upstate New York had been exposed. What should we make of these findings? Here's a few observations, more welcome in the comments.
(1) The infection fatality ratio is lower than the confirmed case fatality ratio--it looks to be well under 1%. That's somewhat hopeful, although I confess if the odds of dying from this are still 1 in 500, rather than 1 in 100, that's still a bet I'd rather not take. (One problem in being more precise is that while we've known that confirmed cases are undercounting, we also know that not all the deaths are being counted either.)
(2) "Herd immunity" requires at least 60% of the population (and maybe 80%) to have immunity, so we're very far from herd immunity, even in a hotspot like New York City.
(3) We don't actually know if the antibodies confer immunity, or, if they do, for how long. There's reason to hope that they confer some immunity for some period of time--recall this earlier post. But that's just a (reasonable) hope at this stage.
(4) It is good news that the vast, vast majority of people exposed to the virus don't get sick enough (if they get sick at all) to require hospitalization, where they would be more likely to join the list of "confirmed" cases (which, again, we know has been undercounting the total amount of infections out there). Despite that, the strain on the healthcare system has been dramatic, and of course would have been catastrophic had no steps been taken to slow the spread.
