From this July Update: https://swprs.org/a-swiss-doctor-on-covid-19/

"On the lethality of Covid-19
Most antibody studies have shown a population-based Infection Fatality Rate (IFR) of 0.1% to 0.3%. The US health authority CDC published in May a still cautious “best estimate” of 0.26% (based on 35% asymptomatic cases).

At the end of May, however, an immunological study by the University of Zurich was published, which for the first time showed that the usual antibody tests that measure antibodies in the blood (IgG and IgM) can detect at most about one fifth of all coronavirus infections.

The reason for this is that in most people the new coronavirus is already neutralised by antibodies on the mucous membrane (IgA) or by cellular immunity (T cells) and no symptoms or only mild symptoms develop.

This means that the new coronavirus is probably much more widespread than previously assumed and the lethality per infection is around five times lower than previously estimated. ...