Listening to the Prof. Drosten Podcast (German only), he highly doubts that they actually had reached herd immunity before their second deadly wave. He rather

Listening to the Prof. Drosten Podcast (German only), he highly doubts that they actually had reached herd immunity before their second deadly wave. He rather assumes something like 40% and then the mutated variant raged on (not badly affecting but infecting the 40% partially, and thus driving the infections).