When you're already using a N95 or better, the filter effectiveness is not the most important thing - the most important thing is fit - how much air leaks around the air filters.

A P100 absolutely helps reduce the risk of infection. But, I would argue that typically the primary way it does so is by improving fit (because most P100s are reusable elastomeric respirators while most N95s are disposables), and only secondarily by filter efficiency.

See my blog post https://firstsigma.substack.com/p/masks if you want a ton of detail on the topic.

The rough rule of thumb I use is that a well-fit N95 reduces Covid risk by a factor of 1/8, while a well-fit P100 reduces Covid risk by a factor of 1/20. Note that this is an estimate of real-world risk, particularly for an untrained person who might not be getting a perfect seal every time they put on the mask. Source: microcovid

A rough Microcovid calculation for the specific scenario you posit in this question gives me a ~1% probability of infection when wearing a P100 - this is for a 1-hour bus ride with 5 unmasked covid-positive passengers sitting ~3 feet away from you, with the windows closed and no air filters in the bus. Airplanes are far lower risk because they have really good air filtration. The same calculation for an N95 gives ~2% probability of infection.

This is pretty close to the 0.5% threshold you specified, and the specific parameters you use (e.g. length of the trip, how densely packed the bus is, etc) would determine whether it's above or below.

@jack Ah, thank you. I will double the subsidy.

What about entry from airborne droplets entering the eyes?

@ooe133 That won't change the market resolution of course (as per the description), I'm just curious about eye transmission.

@ooe133 Doubling the subsidy doesn't really make sense imo. The question as stated is unclear, you could get a YES or NO answer from microcovid depending on which parameters you plug in.

@ooe133 Re eye protection, microcovid says

For users seeking even higher protection than 1/20, we suggest eye protection, including full-face masks, as described in the Respirator assigned protection factors wikipedia page.

But I personally have never bothered with it.

@ooe133 can you provide a citation that N95 masks are insufficient to protect the wearer from airborne viral transmission? I had the understanding that they are, when correctly fitted, but that the general public usually isn’t fit-tested and may also have sloppy practices and imperfect use (e.g. touching the exterior of the mask, reusing and leaving it out btw uses in a manner that could be vector, touching the mask to lift it up for sips of water, …)

I googled and this was the first result: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9947910/

"We conclusively show that the performance of the designed cloth mask is identical to that of a commercially available N95 mask."

No idea if it's reliable as academia is dysfunctional (nowhere near as bad as the major news outlets though).

@ooe133 You are right to be skeptical, that claim is bogus. N95s work better than cloth masks. There's a reason doctors use them. Here are some references to back it up: https://www.microcovid.org/paper/all#masks

I will not bet in this market.