The goal of the study is to get the current situation of the infections in the heavily affected town of Gangelt (12.529 residents) in NRW. They also want see how many people already have antibodies.
They wrote a letter to 600 households. Of those 600 households 400 with 1000 people took part in the study. They were questioned and got tested by swabs and a blood test for the antibodies. They have the results of 500 of those people in and gave a press conference today.
The current results are that ~14% of the tested people in the study had antibodies and ~2% of the people had active Corona infections. The total infection rate was ~15% (currently or already recovered infections).
The CFR from that data + the total infections in Gangelt (the ones that were already active/tested outside of the study) is 0.37%.
They conclude form these first results that 15% of the populace of Gangelt is already immune to the virus and the "herd immunity" is already in progress as a result. They especially say that with 15% immune people, the spread of the virus is already slowed down.
They think that with keeping serious hygiene measures intact, that the viral concentration of a person can be reduced and that as a result the cases are more mild while developing immunity. (I think that is backed up through other studies).
The initial spread through Carnival and Apre-Ski in Ischgl (they could trace pretty much all cases back to those) was a "superspreading event" which should not happen again as long as you keep the stronger hygiene measures.
From the points above (no superspreading events -> better hygiene -> less viral load -> milder cases ) they think that the CFR will be lower in the future.
They then propose a four-phase strategy:
Phase 1: Social quarantine (current phase)
Phase 2: Step by step going back to normal, while keeping stronger hygiene rules intact
Phase 3: No quarantine regulations, but keeping stronger hygiene rules intact
Phase 4: Back to normal