They’ve known this for almost 100 years:

Confronting new, more transmissible variants of the coronavirus and a winter spike in infections, a number of European countries are beginning to make medical-grade face masks mandatory in the hope that they can slow the spread of the disease.

Source: European countries mandate medical-grade masks over cloth face coverings –CNN

Public health continues to undertake, involuntary, non-informed consent medical experiments on the population.

Germany now joins France in required certified masks, Austria and the White House in requiring N95 masks. In a couple of months, we will likely be required to wear hazmat suits with self contained breathing apparatus in order buy groceries.

Coldstreams Skeptic