You don’t need to filter the viruses themselves because they can’t live on their own. In dry air, their proteins denature immediately and they become inactive (unable to cause infection). SARS-CoV-2 is primarily transmitted via respiratory droplets. Initial droplet sizing is ~80um. A cloth mask does just fine filtering most of that. Is it air-tight? No. Does it severely reduce both the volume of respiratory droplets released by an infected person and the distance the remaining droplets travel? Absolutely.
Check out Fig 6-9 here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7301882/
A cloth mask does just fine filtering most of that. Is it air-tight? No. Does it severely reduce both the volume of respiratory droplets released by an infected person and the distance the remaining droplets travel? Absolutely.
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If you believe that we’re fine as long as we use an everyday mask to block droplets, let me challenge to to spend some time with an ebola patient with only droplet protection.