Stop the virus
How safe do I need to be to fully stop the virus?
There's a difference between slowing down the spread of the virus and stopping the virus.
(This webpage is aimed at a general audience, especially schools. FOR A MORE CLINICAL/ACADEMIC ARTICLE, see this comment/article in The Lancet on endcoronavirus.org and a German plan for stopping the virus, commonly known as #CovidZero. Australia also has a #CovidZero style plan where they take 1 case of community infection as 1 too many.)
In the US (Jan 2020), we aren't
even trying to stop the virus right now.
When we re-open schools, we accept that (1) there are some (maybe 3%) of students have the active virus, and (2) there will be some person-to-person transmission. We are willing to open schools because we think the # of expected infections is small enough. That's compared to the harm (to students) of not being in school. That cost-benefit may be accurate, but it hides something: the safety guidelines for schools are about slowing down the spread of the virus and not stopping the virus. In the US (Jan 2020), we aren't even trying to stop the virus right now.
CDC RULES FOR GENERAL PUBLIC
If you want to just slow down the spread of the virus, just follow the CDC 6ft+mask rule. For most, this is okay. Your small risk of infection (probably in the 1 in 10,000 range, as predicted by this aerosol risk calculator) is acceptable, especially if you aren't high risk. However, if you want to stop the virus, I think you need something like (1) 99.9%+ mask protection coupled with (2) ventilation and (3) avoiding crowds.
When the CDC says to wear a mask and distance 6ft, that's slowing down the virus, not stopping it.
HIGH RISK SITUATIONS HAVE DIFFERENT RULES
In a high-risk situation (like a COVID-19 hospital or a nursing home), they'd never do just Masks and 6ft.
In high risk hospitals, workers use N95s or better equipment because they are aiming at a higher standard: stopping the virus. And, even there, many hospitals and nursing homes have had outbreaks. And, not just in the USA. In the UK, where they pay their workers better, have better standards, and use better PPE, they still have these outbreaks. The unfortunate conclusion:
Even an N95 is not enough to stop infection
in high risk places like nursing homes.
Evidence? Places with N95 and good protocols
are still seeing infections.
Don't get me wrong... masks do work and help. And the infections would likely be 10x worse if people didn't have N95s and were just wearing cloth masks. The whole point is it doesn't stop the virus. The question then is: Can we stop the virus, and not just slow it down?
Yes! You can stop the virus*. Wear a viral helmet that has 99.99% or higher efficiency and you'll let in 500X less particles than an N95. Getting beyond 95% filtration is so important. You can build the best protection available for $15.
Another reason to wear a viral helmet is because of super spreaders. You want something that stops the virus in 100 out of 100 cases. Even the worst cases, where someone is really infectious (and probably asymptomatic too, so your guard is down). What does it mean to go 100 for 100?
Take 100 cases of COVID.
The middle person of infectiousness (person #50), might have a virus concentration of 1,000. And a normal mask will protect well against them. A viral helmet is probably overkill.
The most infectious person (person #100), would have a virus concentration of 10,000,000 or 10,000 times more. A normal mask will still help protect, but it won't do enough. With that many more particles, it's possible a few virus particles get through in the superspreading/highly infectious case. A viral helmet is no longer overkill. It's the right tool for the situation.
So, if you want to go for perfect (protecting in 100 out of 100 cases) and really stop the virus, use the best protection: 99.99%. And couple a mask with other protective activities. Use a numerical aerosol risk model (link, link, link) to help you gauge the effectiveness of each measure.
*technically speaking, even 1 in a billion risk is not "stopping the virus". Hence, 99.99% filters will not technically achieve "stopping the virus". However, they get you much closer than the minimum CDC rules. Viral Helmets + ventilation + avoid crowds + decrease time indoors--- all these together can get you to where your risk is less than 1 in 10million for all of 2021. Just doing 6ft and a casual mask might mean your chance of getting COVID in 2021 is around 1-50%... and that's just too high.