How Much Does Your Mask Protect You if Others Aren't Wearing One?
"If you're the only one with a mask on, are you still protected? Here's what experts say about mask effectiveness and COVID risk on public transit.
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What the experts say
"The short answer is yes," says Dr. Reynold Panettieri, Jr, a critical care physician and Professor of Medicine at Robert Wood Johnson Medical School -- it is worth it. "The long answer is that it's not as effective as everyone else wearing a mask."
Wearing a cloth mask reduces your risk of catching COVID-19 by about two-fold, he says, whereas a disposable surgical mask is between "five- and seven-fold better." NIOSH-approved N95 respirators provide the most protection, according to the US Centers for Disease Control and Prevention, when they're worn properly and sealed snugly to your face.
Dr. Taylor Nelson is an osteopathic infectious disease physician at the University of Missouri Health Care. She said in an email to CNET that protection varies on the type of mask, but also how well it fits.
"Multilayer cloth masks can limit about 50 to 80% of small particles from escaping when someone coughs," Nelson says. "On the other hand, the same quality of mask may prevent up to about 50% of these particles when the exposed person is wearing a mask while the infected person is not."
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What the research says
A CDC report from February 2021 on mask effectiveness using simulated respiratory droplets found that "double-masking" by layering a cloth mask over a surgical mask decreased a person's exposure in a no-mask/mask situation by 83%. For a person wearing a "knotted and tucked" medical mask, which tightens the seal around your nose and mouth, there was a 64.5% decrease in exposure. (Check out this CDC video on how to knot and tuck a surgical mask correctly.)
In the CDC's simulation study, a regular surgical mask provided only 7.5% protection for the wearer. Another simulation study from Japan found cloth masks offered a 20% to 40% reduction in virus uptake compared to no mask, with N95 masks providing the most protection for the wearer (80% to 90% reduction).
Broadly speaking, people who always wear masks indoors are less likely to test positive for COVID-19 than people who do not, according to a February report by the CDC. People who reported wearing cloth masks had 56% lower odds, people who wore surgical masks had 66% lower odds and those who reported wearing a KN95 or N95 had 83% lower odds. A big qualifier noted in this report, however, is that people who report wearing masks indoors might be more likely to take other protective measures that help prevent COVID-19 infection, such as avoiding crowded areas when possible."
https://www.cnet.com/health/medical/how-much-does-your-mask-protect-you-if-others-arent-wearing-one/
= new reply since forum marked as read
When masks were still required (remember the good old days...last year) I'd see sloppy fitting masks, or, guys with full beards having only the little patch around their mouth and nose covered. Like a fig leaf on a nude. 
I can't control what others do, but I can protect myself and my wife as much as possible. 