Long time ago [cue banjo music] I had a job where we intermittently wore particle masks in areas with asbestos. No idea what the filtration rating was, the filter portion was replaced after one shift of use and the housing was cleaned and reused. They worked reasonably well WRT fit and comfort.

Anyhoo, it had a one-way valve that opened on exhale and closed on inhale, because the issue was not us exhaling asbestos at others. Contagious disease is potentially two-way so such a valve wouldn't be appropriate.