What is the overall infection fatality ratio (IFR) of #SARSCoV2 in Germany? The widely discussed Gangelt study now got published in @NatureComms. There are a number of issues with its estimate of the IFR. A thread. (1/n) nature.com/articles/s4146…
What do we already know about the IFR in Germany? At @ISPMBern, we published a modeling study that estimates the IFR at 0.8% (95% CI: 0.5%-1.1%) for Bavaria and 0.7% (95% CI: 0.5%-1.3%) for Baden-Württemberg based on 1,049 and 802 deaths. (2/n) journals.plos.org/plosmedicine/a…
The IFR can also be estimated from seroprevalence studies. A recently published report from Munich (Bavaria) found an IFR of 0.8% (0.6%-1.1%), confirming our earlier estimates. (3/n) klinikum.uni-muenchen.de/Abteilung-fuer…
So let's have a look at the Gangelt paper. In general, this is a well done study investigating an early outbreak of #SARSCoV2 in a small community of 12,597 people. They estimate an infection attack rate of 15.5% corresponding to 1,956 people. (4/n)
Then, they estimate the IFR based on 7 deaths (7/1956 = 0.36%). You might say: Wait, what? How can you estimate an IFR based on 7 deaths only? Doesn't chance come into play here? You're right. With such a small number of deaths, you can't get precise estimates of the IFR. (5/n)
Assuming binomial sampling, one obtains a 95% CI of 0.14%-0.74%. While the authors report such a CI in the main text, they hide it for the numbers in the abstract. What is the rationale of presenting numbers with a precision that does not exist? This is somewhat concerning (6/n)
But there is more. According to this article from @hfeldwisch, they did not include all deaths that stem from infections up until the end of the study period. Instead of 7, there were probably 13 deaths. (7/n) medwatch.de/2020/11/26/die…
This would result in an IFR of 13/1956 = 0.66% (95% CI: 0.35%-1.13%). That's interesting, because this estimate is in good agreement with the results from our statistical modeling study and the seroprevalence study from Munich. (8/n)
While that's an interesting turn of events, I still would not put too much trust into an IFR from such a small community and with such a small number of deaths. Especially when there are much bigger studies around that are based on hundreds or thousands of deaths. (9/n)
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