It's a rather hodgepodge of information presented there in a confusing set of numbers and they don't really discuss homemade masks, which is what a large portion of the population is doing. And they stress the effectiveness of N95 respirator.
When talking masks they say the base transmission rate is 17.4% and with medical grade N95 drops to 3.1%.
When talking social distancing they say the base transmission rate is 12.8% and with 3-6 feet social distancing drops to 2.8%.
When talking goggles and face shields they say the base transmission rate is 16% and with goggles drops to 5.5%.
So playing devils advocate based on their numbers, absent medical grade masks, social distancing and goggles could give better protection than cheap homemade masks.
Originally Posted by eccielover
They were mostly looking at transmission rates from exposed individuals (patients with SARS, MERS or Covid-19) to health care workers. The 3.1% is for face masks in general, not just N95. They say it was for "N95 or similar respirators or face masks (eg disposable surgical masks or similar reusable 12-16 layer cotton masks.". They do say the N95 works better than the surgical mask which works better than the cotton mask.
As we've discussed a lot here, if you wear a mask, the benefit is primarily for other people, not you, unless maybe it's an N95. They were looking at transmission the other direction, from the infected person to health care workers. Presumably if they had been able to study transmission from the mask wearer to others, the transmission rate would have been reduced by more than the 82% (from 17.4% to 3.1%) in the paper.
And yes, it looks like social distancing is about as effective as wearing a mask, to reduce your own risk of getting the disease. I'll add that they had more confidence in their results from looking at the social distancing studies than the mask studies.
You probably know the reproduction number for a disease, or "R", is the number of people on average that are infected by one carrier. The initial value of R, which is called Ro, may be anywhere from 2.5 to 5 for Covid-19 based on various estimates. So on average, at the onset of the epidemic before doing anything to control the spread, on average a person will transmit the disease to 2.5 to 5 other people.
If R falls below 1 and stays below 1, then the disease will die out.
If you're getting, say, a 50% reduction in R by wearing masks (I think it would be more) and another 50% by staying 6 feet away from others, you've got this licked -- 0.5 x 0.5 = 0.25, so if I'm thinking about this correctly that's a 75% reduction in R. The effects on the economy would be very positive. One of the papers referenced in the Business Insider article referred to something like that: "When facemasks are used by the public all the time (not just from when symptoms first appear), the effective reproduction number, [R value], can be decreased below 1, leading to the mitigation of epidemic spread." Another described infections falling to almost "0" in a German town after people started using masks.
To get this to work, I suspect most people need to do it. See the article about the ship in the article. The person who just wears the mask or who just follows social distancing guidelines will have a lower chance of getting the disease, but to really knock this out you've got to have have a lot of people doing it.
