COVID-19’s “contagion probability” between two people is 70% if the carrier is not masked, 5% if the carrier is masked, and 1.5% if both parties are.
— a viral image circulating on social media since April
A popular social media post that’s been circulating on Instagram and Facebook since April depicts the degree to which mask-wearing interferes with the transmission of the novel coronavirus. It gives its highest “contagion probability” — a very precise 70% — to a person who has COVID-19 but interacts with others without wearing a mask. The lowest probability, 1.5%, is when masks are worn by all.
The exact percentages assigned to each scenario had no attribution or mention of a source. So we wanted to know if there is any science backing up the message and the numbers — especially as mayors, governors and members of Congress increasingly point to mask-wearing as a means to address the surges in coronavirus cases across the country.
Doubts About The Percentages
As with so many things on social media, it’s not clear who made this graphic or where they got their information. Since we couldn’t start with the source, we reached out to the Centers for Disease Control and Prevention to ask if the agency could point to research that would support the graphic’s “contagion probability” percentages.
“We have not seen or compiled data that looks at probabilities like the ones represented in the visual you sent,” Jason McDonald, a member of CDC’s media team, wrote in an email. “Data are limited on the effectiveness of cloth face coverings in this respect and come primarily from laboratory studies.”
McDonald added that studies are needed to measure how much face coverings reduce transmission of COVID-19, especially from those who have the disease but are asymptomatic or pre-symptomatic.
Other public health experts we consulted agreed: They were not aware of any science that confirmed the numbers in the image.
“The data presented is bonkers and does not reflect actual human transmissions that occurred in real life with real people,” Peter Chin-Hong, a professor of medicine at the University of California-San Francisco, wrote in an email. It also does not reflect anything simulated in a lab, he added.
Andrew Lover, an assistant professor of epidemiology at the University of Massachusetts Amherst, agreed. He had seen a similar graphic on Facebook before we interviewed him and done some fact-checking on his own.
“We simply don’t have data to say this,” he wrote in an email. “It would require transmission models in animals or very detailed movement tracking with documented mask use (in large populations).”
Because COVID-19 is a relatively new disease, there have been only limited observational studies on mask use, said Lover. The studies were conducted in China and Taiwan, he added, and mostly looked at self-reported mask use.
Research regarding other viral diseases, though, indicates masks are effective at reducing the number of viral particles a sick person releases. Inhaling viral particles is often how respiratory diseases are spread.
One recent study found that people who had different coronaviruses (not COVID-19) and wore a surgical mask breathed fewer viral particles into their environment, meaning there was less risk of transmitting the disease. And a recent meta-analysis study funded by the World Health Organization found that, for the general public, the risk of infection is reduced if face masks are worn, even if the masks are disposable surgical masks or cotton masks.
The Sentiment Is On Target
Though the experts said it’s clear the percentages presented in this social media image don’t hold up to scrutiny, they agreed that the general idea is right.
“We get the most protection if both parties wear masks,” Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who studies viral air droplet transmission, wrote in an email. She was speaking about transmission of COVID-19 as well as other respiratory illnesses.
Chin-Hong went even further. “Bottom line,” he wrote in his email, “everyone should wear a mask and stop debating who might have [the virus] and who doesn’t.”
Marr also explained that cloth masks are better at outward protection — blocking droplets released by the wearer — than inward protection — blocking the wearer from breathing in others’ exhaled droplets.
“The main reason that the masks do better in the outward direction is that the droplets/aerosols released from the wearer’s nose and mouth haven’t had a chance to undergo evaporation and shrinkage before they hit the mask,” wrote Marr. “It’s easier for the fabric to block the droplets/aerosols when they’re larger rather than after they have had a chance to shrink while they’re traveling through the air.”
So, the image is also right when it implies there is less risk of transmission of the disease if a COVID-positive person wears a mask.
“In terms of public health messaging, it’s giving the right message. It just might be overly exact in terms of the relative risk,” said Lover. “As a rule of thumb, the more people wearing masks, the better it is for population health.”
Public health experts urge widespread use of masks because those with COVID-19 can often be asymptomatic or pre-symptomatic — meaning they may be unaware they have the disease, but could still spread it. Wearing a mask could interfere with that spread.
Our Ruling
A viral social media image claims to show “contagion probabilities” in different scenarios depending on whether masks are worn.
Experts agreed the image does convey an idea that is right: Wearing a mask is likely to interfere with the spread of COVID-19.
But, although this message has a hint of accuracy, the image leaves out important details and context, namely the source for the contagion probabilities it seeks to illustrate. Experts said evidence for the specific probabilities doesn’t exist.
We rate it Mostly False.
–Victoria Knight, Kaiser Health News and PolitiFact
FlaglerLive relies on a strong core of donors. But they’re just a fraction of the 25,000 readers who daily depend on FlaglerLive for reliable, fearless reporting and analysis you cannot get anywhere else. If you’re still on the sidelines, we need you to join the Friends of FlaglerLive today. Elections, storms, the latest catastrophe - when dependable and factual local reporting will be more essential than ever, take a stand for integrity and have a direct voice in fostering serious journalism in your community. As little as $10 makes a difference, or better still, become a monthly donor: Become a "Friend of" FlaglerLive, a 501(c)(3) non-profit news organization. Donations are tax deductible. Think of it as buying a "scoop", in every sense of the term!
Reader Interactions
Comments
Leave a Reply
This site uses Akismet to reduce spam. Learn how your comment data is processed.
Fredrick says
CDC numbers from last week. 71 total deaths from C19 in the US. That includes deaths of those with underlying conditions athat had hours, minutes, days or months to live. The week before it was 464. The 71 I am sure will be adjusted up some as last weeks was. I am sure that number is going to go through the roof though because of the 10’s of thousands that were protesting in close proximity of each other over the last month. Oh wait correction. I forgot that does not spread the covid. I am sure it will spike because of trump rallies, people going to church, and people enjoying the beach and outdoors.
Also waiting for the local hospital cases to spike….. still at 33 admissions since the start of this. Of course its going to go up some. We opened things back up. The reason we destroyed the economy, made people lose everything they have worked for including homes and businesses, was to not overwhelm the healthcare system. Each confirmed test keeps bringing the mortality rate further and further down. Protect the vulnerable and stop the hysteria and fear mongering. Life is a risk…. Get on with it.
Mythoughts says
If it isn’t written by a medical professional I am not buying it nor should anyone else. It is really a shame our local, state, and federal government isn’t listening to the medical professionals and put a mandatory on everyone wearing masks in public.
I guess everyone is waiting for more deaths to happen.
Percy's mother says
5 deaths since March.
That’s just over 1 death a month.
AND, we don’t really know if those 5 deaths were due to underlying comorbidity (morbid obesity, diabetes, smoking, COPD, heart disease/failure, old age, Alzheimer-related, kidney failure, cancer, asthma, etc.).
Concerned Palm Coast Resident says
Way to go. Rather than try and provide clarity while keeping the general message of the fact they do indeed help, you closed out the piece by essentially debunking the effectiveness of wearing a face covering.
Thanks. Looking forward to eventually seeing our numbers continue to rise and probably missing 2 weeks of work (and possible a few days in the hospital, which will leave me with medical bills I don’t need) when my mask-wearing self gets sneezed on by a non-mask wearing infected person who refuses to wear one.
Thanks a bunch.
George says
Amen! Everyone needs to wear a mask! Flagler County needs to move forward with mask wearing madate with fines for those who refuse. We emplore our local sherriff to protect us as he swore and enforce the mask mandate! If not we the citizens can legally make citizens arrests in public as per Florida law.
Trailer Bob says
I keep saying, try the plastic face shields that cannot be breached as easily as face (mouth, nose) masks.
Of course you still will not want to give up on social distancing, as someone within six feet, exposing you to their breath could still effect you from the side of your face. OR, you could do both. I am not there yet though. Stay safe.
Willy Boy says
Yep. It’s what you see the health professionals wearing, and they should be available to the public at no cost and made mandatory, but it’ll never happen.
Trailer Bob says
I bought about 25 of them online for $2.50 each.
The cloth mask is a disaster waiting to happen. Provides false hope. Doesn’t protect your eyes from droplets, harbors the disease. And how the hell do you drink a beer?
Jimbo99 says
Just me, the mask is only immediate protection from the onslaught of initial coronavirus droplets. It’s like any filtration system that initially traps even dust. As one breathes the particles are worked into the fibers, ultimately working themselves thru the filter completely. How long after the contamination is it before the filter doesn’t trap anything ? All that is even predicated that the fibers of the filter are tight enough to block the virus and whatever other debris is airborne. One doesn’t need to study this to be an expert on it. It’s absurd to think that anyone would call themselves an expert for thinking about this for anything more than a few hours tops. Filters have been used in HVAC systems and in our car for about a century. Why do you need to change the air filter in your home or car periodically ? Those filters trap dust particles and anything else that is in the air, they either clog or they become ineffective and the dirt still gets into the cleaner machinery. The day when you stop dusting the furniture in the house is a general indication the filter actually works. Otherwise it’s a efficiency rating at best.
Percy's mother says
I find it interesting that people are up in arms and hysterical about forcing the issue regarding masks but, in general, most people don’t give a damn about their health on a daily basis.
All you have to do is go to Publix to see how sick the general population is: Gray complexions, dull eyes, barely able to trudge from the car into the store, dosed up on a myriad of pharmaceutical drugs, grossly overweight and out of shape, grocery cards laden with garbage packaged food and overall outwardly obviously lacking from nutrition (vitamins and minerals), i.e., “malnourished”.
There’s a small segment of the population that does care about health and well-being, but very few, I’d day about 5%.
To be healthy with a healthy immune system, it takes consistent and thoughtful WORK, DAILY, and that means healthy food (plant-based diet with minimal protein), no sugar, carbs only from veggies, no grains, no alcohol, good fats, minimal caffeine along nutritional supplementation with pharmaceutical-grade products (not the stuff you buy over-the-counter in Publix or Walmart). People just want to treat their bodies like hell and “take a pill” when they get sick.
But heaven forbid these same people who don’t give a damn about their health on a daily basis (95% of the population) are screaming about everyone wearing a mask.
If you live healthy on a daily basis, eat as noted above, take high quality nutritional supplementation, limit ALL negative media (mental component), exercise daily (find a physical activity you enjoy and/or love so it won’t be drudgery), work on spiritual life (spiritual component), your immune system will be able to fight off most illness and the need for pharmaceutical drugs will be limited.
And by the way, should anyone want to say I’m not a “medical professional”, I’d be happy to supply my (legitimate) credentials.
Trailer Bob says
You may be a medical professional, but you certainly are not a statistician. Quote “There’s a small segment of the population that does care about health and well-being, but very few, I’d day about 5%.”
So if we have 100 people in a room, only 5 of them eat right, stay in shape, wash their hands, etc.?
No, you are not a statistician. But hey, nowadays anyone can say anything, correct or not.
Barney Fife says
Well George try to make a citizen arrest and you will need the mask to catch the blood and prevent the spread of blood born pathogens. That tactic will both increase the er and jail work load since on of us would be going to the hospital and the other jail.