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https://www.spectator.co.uk/article/covid-antibody-test-in-german-town-shows-15-per-cent-infection-rate-0-4pc-death-rate
Another antibody + antigen test from the town of Gangelt, in Germany. 1,000 people from 400 households. 2% currently infected, 14% tested positive for the antibodies. That's three times whad had originally been expected. Estimated TFR from finished cases was 0.37%, but no information about ages was given.
On the other hand, a study from China claims 6% of positive antibody tests had results that were difficult to confirm. This means either that a small percentage of the population might not have built a decent degree of immunity even after infection, or perhaps the test itself wasn't as sophisticated as it would've been necessary. Another possibility is that, at least for some people, the antibodies take more time to build up (a common feature of immunosenescence and some diseases).
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