As usual, a great write up. I think one nuance that is important is: > Does letting a single influenza virus through mean you will get infected? If so, any re

As usual, a great write up. I think one nuance that is important is: > Does letting a single influenza virus through mean you will get infected? If so, any reduction short of 100% is useless. I have a vague sense that this isn’t true; your immune system can fight off most viruses, and the fewer you get, the better the chance it will win. Also, even respirators don’t claim to reduce particle load by more than 99% or so, and those work, so it can’t be that literally a single virus will get you I was speaking with an ER doctor yesterday who said that aside from comorbities and age, the single biggest predictor of how severe a case may be is the viral load exposure. The reasons that N95 respirators are so important in a hospital setting is that when a dr or nurse are continuously exposed to the virus, those deltas in performance might mean they pstill get sick, but it’s mild and back to work in two weeks vs ending up in the hospital for a month.