From a preliminary analysis by scientists in the hard-hit Heinsberg region in Germany (on the Dutch border) in the town of Gangelt, where that February 15, 2020 Carnival party I mentioned yesterday acted as a superspreader event:
Procedure: A serial letter was sent to about 600 households. In total, about 1000 inhabitants from about 400 households took part in the study. Questionnaires were collected, throat swabs taken and blood tested for the presence of antibodies (IgG, IgA). The interim results and conclusions of approx. 500 persons are included in this first evaluation.
Preliminary result: An existing immunity of approx. 14% (antiSARS-CoV2 IgG positive, specificity of the method >.99 %) was determined. About 2% of the persons had a current SARS-CoV-2 infection detected by PCR method. The infection rate (current infection or already been through) was about 15 % in total. The case fatality rate in relation to the total number of infected persons in the community of Gangelt is approx. 0.37 % with the preliminary data from this study. The lethality rate currently calculated in Germany by Johns-Hopkins University is 1.98 %, which is 5 times higher. The mortality in relation to the total population in Gangelt is currently 0.15 %.
Preliminary conclusion: The lethality calculated by Johns-Hopkins University is 5 times higher than in this study in Gangelt, which is explained by the different reference size of the infected persons. In Gangelt, this study covers all infected persons in the sample, including those with asymptomatic and mild courses. In Gangelt, the proportion of the population that has already developed immunity to SARS-CoV-2 is about 15%. This means that 15% of the population in Gangelt can no longer become infected with SARS-CoV-2, and the process has already begun until herd immunity is achieved. This 15% of the population reduces the speed (net reproduction rate R in epidemiological models) of a further spread of SARS-CoV-2 accordingly.
So, an infection fatality rate of 0.37%, which is likely to go up over time to, say, 0.5% (just me speculating from the Diamond Princess history) under strong German health care conditions without the hospitals overwhelmed.