San Francisco Chronicle - (Sunday)
FACING THE FACTS: MASKS BEST DEFENSE
Covering mouth, nose top method to control spread, scientists agree
Months into the coronavirus pandemic, not only is the disease still spreading but so is the cultural warfare in response to the virus. Few things have ignited more hard feelings than the use of face masks.
But the science is clear: Wearing masks helps reduce the spread of the virus. If enough people wear masks consistently — experts and studies peg the magic number to be at least 80% of the population — it will significantly slow transmission.
It’s difficult to determine exactly how much widespread mask usage would impact the spread of the virus. This is, in part, because states and counties vary greatly in other policies that also affect transmission, such as social distancing and economic reopening strategies. And it’s not possible to do random, controlled trials of mask usage during the pandemic because it would be unethical to ask one group of people to wear masks and another not to.
But substantial scientific evidence and modeling of mask usage have led to over
whelming consensus in the medical community that wearing masks is the best lowcost, lowtech, accessible action every member of the public can take to help contain the spread of the deadly virus.
Given a choice between the three most widely recommended infection prevention tools — wearing a mask, washing one’s hands and social distancing — wearing a mask is the most important, said Dr. Peter ChinHong, an infectious disease physician at UCSF.
“I couldn’t be more enthusiastic,” ChinHong said. “The bulk of evidence suggests the most important thing you can do is wear a mask. Forget about cleaning your phone every 10 seconds.”
Masks offer some protection to the person wearing it if, say, an N95 mask fits properly. But in terms of controlling the pandemic at the population level, the more important function of masks is to protect people around the wearer by blocking virusbearing droplets from getting into the air and infecting them. This is especially critical because asymptomatic, or presymptomatic, people account for nearly half of all coronavirus infections. Those people could be unknowingly spreading the virus to others. Surgical masks and cloth masks both work to block droplets from being emitted.
“It’s far more effective to prevent at the source,” said De Kai, a researcher at UC Berkeley’s International Computer Science Institute and professor at Hong Kong University of Science and Technology, which has modeled the use of masks and reductions in virus transmission. “Otherwise you spray it all over, it’s aerosolized and hangs in the air so other people who are wearing masks might still get it through their eyes. Cut it off at the source. This is why it has been so effective in East Asia when you have entire populations wearing masks.”
Regions accustomed to wearing masks like Hong Kong and Taiwan — which have each reported just seven deaths during this pandemic — are managing the virus far better than countries that don’t. About 98% of Hong Kong residents say they wear masks when leaving their home during the pandemic, according to a May study in the medical journal the Lancet.
Dozens of studies suggest that the widespread use of masks helps contain viral spread, including: An April New England Journal of Medicine study shows that mouth coverings prevent nearly all droplets from being emitted when the person wearing one is speaking. A June study by Virginia Commonwealth University shows that countries with cultural norms, or government policies, supporting maskwearing had much lower coronavirus mortality rates than countries that do not. The study looked at 198 countries and found that countries that use masks widely saw percapita mortality increase by an average of only 8% each week, compared with 54% in countries that do not. A June study in the health care journal Health Affairs shows that mask mandates in 15 states and the District of Columbia helped avert as many as 23,000 to 450,000 new cases between April and May. An April study by Yale shows that countries where people commonly wear masks when sick — including South Korea, Japan, Hong Kong and Taiwan — had an average daily growth rate of confirmed cases of 10%, compared with 18% in countries without such mask norms. The growth rate of deaths in countries with mask norms was 11%, compared with 21% in countries without mask norms. A simulation by researchers at UC Berkeley and Hong Kong’s University of Science and Technology found that in one scenario in the United Kingdom, if 80% to 90% of people wore masks, it would lead to significantly fewer deaths than if just 50% of people wore masks — 60,000 deaths, compared with 240,000 deaths.
Wearing a mask is something that is within each person’s control, whereas you can’t always control how much distance there is between yourself and others, said ChinHong of UCSF. He noted that, in Hong Kong and Taiwan, crowds of people at crosswalks and streets aren’t always social distancing but they are almost always wearing masks.
“Masks trump everything else because you can control that,” ChinHong said. “You can’t control that distance, many times.”
Experts also point to two recent case reports that appear to demonstrate that if sick people wear masks — even in enclosed indoor spaces, for extended periods of time — they will not spread the virus to others.
In one case, a man traveling from China to Canada in January had a dry cough during the 15hour flight and later tested positive for the coronavirus. None of the 25 passengers who were sitting closest to the man, and no flight attendants, tested positive.
In another case, in May, two hairstylists at a Great Clips in Springfield, Mo., were diagnosed with the coronavirus after they’d come into close contact with a combined 140 customers over the course of nine days. Both hairstylists wore masks the entire time, as did customers, and no infections were reported among the customers — though only about a third got tested.
“If you need any more proof than that, you’re a Luddite,” said UCSF epidemiologist Dr. George Rutherford.
Bay Area residents appear split. On a recent Friday afternoon in downtown Walnut Creek, Jennifer Stowell, a 30yearold marketer, did not wear a mask, saying COVID19 is “just a drop in the bucket compared to the extensive levels of toxicity all around us that’s manmade . ... Just on my one walk now I’ve breathed in tons of toxics.
“The best way to handle this? There’s a thing called natural law — inspiring people to have a choice over your health,” she said. “If you’re older, stay away from sick people, but also bolster yourself so you’re healthy enough to build resistance.”
But at a sushi restaurant nearby, coworkers Chadwick Manning and Argun Vasan were eating lunch at a curbside table and put on their masks every time anyone stopped by to talk.
“We’re not done with this virus at all,” said Vasan, 35.
“This is clearly the event of our lives, and we have to do what’s safe. Wear a mask.” Widespread mask usage would work nearly as well as a vaccine if everyone or almost everyone did it, several medical and infectious disease experts said.
Still, California did not issue a mask mandate until midJune. Gov Gavin Newsom was asked several times Thursday how the state plans to enforce the mask mandate, and he said there would be some enforcement but hopes Californians comply on their own.
“Look, we’re not going to everybody’s backyard and enforcing. You know that,” Newsom said. “Consider others. That could be your mother, it could be your grandmother, it could be someone you deeply love.”
Part of the problem is that many leading public health agencies, including the World Health Organization, the U.S. Surgeon General’s Office and the CDC initially discouraged the public from wearing masks at the start of the epidemic, in part because there were shortages of masks for health care workers. The CDC didn’t recommend masks for the public until April, and the WHO didn’t recommend masks until June. That bungled the early messaging around whether people should wear masks or not.
“We just have to be as good as Madison Avenue,” said Dr. Yvonne Maldonado, a Stanford epidemiologist. “Public health just doesn’t have those amount of dollars. If we can get people to buy into masks the way we get them to buy into, name your product, we’d do fine . ... If we could just get everyone to wear a mask for a few weeks, we’d get this thing down really low.”
Catherine Ho is a San Francisco Chronicle staff writer. Email: cho @sfchronicle.com Twitter: @Cat_Ho