It's in the article .
The term "dark matter" is more familiar in cosmology. In cosmology, it is taken to represent something you surmise exists (because the final outcome pretty much requires it to, with your current understanding), but you can neither observe it, nor definitively know what it is.
In the German case, Friston is taking the outcome (very low apparent death rate), which he can't account for it with the known data. So he's invoking some unknown factor (s) ; the "dark matter".
His guesses at what this dark matter is, are :
- People who are isolated enough to be beyond realistic chance of infection;
- People with some form of natural / preexisting immunity.
I think?
