Originally Posted by
dubbin
[citation needed]
http://www.ncbi.nlm.nih.gov/pubmed/22460981/
Tightly sealing a mask to the face blocked entry of 94.5% of total virus and 94.8% of infectious virus (n = 3). A tightly sealed respirator blocked 99.8% of total virus and 99.6% of infectious virus (n = 3)
Ignoring the low n numbers, this is pretty convincing evidence of the efficacy of face masks.
HOWEVER, they didn't assess infection rates - ie does a 90% reduction in virus prevent infection? Most virologists will say no.
It's like trying to vacuum dust from your home, or putting plastic sheeting on your mattress. They dramatically reduce exposure to allergen, but not enough to have an impact on symptoms under clinical conditions.