San Francisco Chronicle - (Sunday)

Experts split over masks outdoors

- San Francisco Chronicle staff writer Erin Allday contribute­d to this report. Aidin Vaziri is a San Francisco Chronicle staff writer. Email: avaziri@sfchronicl­e.com

of outdoor masking in recent weeks, joining a cohort of experts from across the country who suggest that they’re unnecessar­y and overly restrictiv­e at this stage of the pandemic.

Opinions from other Bay Area experts, however, indicate that such consensus is not at all clearcut.

While several states have already eased the rules for face coverings, indoors and outside, California’s Department of Public Health still requires masking in all public settings when people are closer than 6 feet to anyone not from their households. State officials say it is unlikely that policy will change before the state’s targeted June 15 date to reopen most activities.

Gandhi says there is no need to wait.

“I think we could do it now,” she said, though she still advocates for face coverings indoors until newly vaccineeli­gible younger age groups have time to get their shots.

Some experts, however, say that dropping the outdoor mandate would be moving too quickly.

“We have 30 of the 50 states showing an uptick in cases. We’re averaging over 65,000 new cases a day. We’ve got a more infectious variant that is now the dominant strain. The bottom line is it’s not clear what direction the United States is going in,” said Dr. John Swartzberg, an infectious disease expert at UC Berkeley. “This would be an imprudent time to get rid of mask mandates.”

The risk of virus transmissi­on is lower outdoors, but it’s still a risk — one that increases the longer you are around another person.

“To me, it is not about treating indoor versus outdoors as a binary,” said Dr. Peter ChinHong, an infectious disease expert at UCSF.

“Most people already make that risk assessment: Wearing a mask may be less important when there are no crowds around on the street, while jogging on Ocean Beach, or in Golden Gate Park looking at the buffaloes,” he said. “It seems foolish not to wear a mask waiting in a crowded line for takeout, hustling for organic vegetables at a popular stall on a peak farmers’ market Saturday morning, or in a mosh pit at Coachella. Context is everything.”

All counties must abide by the California mask mandate, but they can institute local rules that are more strict. Some Bay Area counties have done that but they’re mostly aligned with the state. San Francisco recommends people put on a face covering outside when they are approachin­g someone within 30 feet, but technicall­y its mandate only requires them within 6 feet of others, which is the same as the state rule. In February, Santa Clara County dropped a local rule requiring people wear masks outdoors at all times, regardless of whether they were around others.

The state mandate could be revised and loosened to require masks only in certain situations outdoors rather than any time others are around. It could stop requiring them on hiking trails and beaches, for example, as long as people aren’t lingering too close together. But state officials have given no sign they plan to do that.

An analysis of five global studies conducted by UCSF infectious disease experts determined that less than 10% of all coronaviru­s infections occurred outdoors. The odds of indoor transmissi­on are nearly 19 times greater. Dr. Nooshin Razani, one of the UCSF researcher­s, said the outdoor number could be even lower since many documented infections occurred over extended time at constructi­on sites and summer camps. But the UCSF paper comes with a caveat: Relaxed mitigation measures could make

How the coronaviru­s spreads

The coronaviru­s dwells in the mucus lining respirator­y passageway­s. When a person breathes or talks, air carrying mucus is exhaled. Vocal cords and the tongue and lips break the mucus into droplets, which cause infection when they are inhaled or deposited on mucous membranes.

DROPLET TRANSMISSI­ON

Coughs and sneezes can propel droplets of saliva and mucus.

The larger droplets in the expelled air fall to the ground quickly and typically don’t travel farther than 6 feet from their source.

EFFECTIVEN­ESS OF MASKS

The highest risk of droplet and aerosol transmissi­on occurs indoors, especially in spaces with inadequate ventilatio­n. Experts agree that wearing a mask in crowded spaces near people talking, shouting or singing can reduce the risk of transmissi­on.

TIMES GREATER

outdoor settings less safe.

Public health experts believe that masks are one of the most effective ways to prevent the spread of the coronaviru­s that causes COVID19, which travels through microscopi­c respirator­y droplets when an infected person sneezes, coughs, talks, laughs or exhales. Masks block or limit exposure to those viral particles.

Outside, these particles are more susceptibl­e to the elements, easily breaking apart under wind, rain and humid

AIRBORNE TRANSMISSI­ON

Tinier particles, produced by talking, shouting or singing, are suspended in the air for longer and travel farther.

Unlike droplets, aerosols can remain airborne for several hours and may accumulate, especially in poorly ventilated indoor spaces. The virus is transmitte­d when another person inhales these aerosols.

CONTAMINAT­ED SURFACES

Respirator­y droplets can also land on surfaces and objects. People could get COVID-19 by touching a surface or object that has the virus on it and then touching their mouth, nose or eyes. This is less common than other ways that the virus spreads.

INDOORS VERSUS OUTDOORS

Virus transmissi­on risk is lower outdoors. Respirator­y droplets and aerosols are more susceptibl­e to the elements. Airflow can help disperse viral droplets and prevent infection. Opinions vary on the need for masks in open spaces. ity. Airflow can help disperse viral droplets and prevent infection as long as people are not near each other for an extended period.

“The virus is trying to jump from someone who is infected. The wind creates turbulence and disrupts the path of the virus,” ChinHong said.

So passing a maskless jogger on a sidewalk is relatively low risk, but passing a large group of unmasked people in the park, or stopping to chat with an unmasked friend on a hiking trail, could be dicier.

The University of Washington’s Institute for Health Metrics and Evaluation estimated that face coverings can reduce a person’s risk of infection by about 40%.

When Gov. Gavin Newsom announced plans to lift most of California’s COVID19 restrictio­ns as of June 15, there was one notable exception: the indefinite mask mandate to protect those who will not be immunized soon. Mainly that will mean children.

“It’s the most powerful and important nonpharmac­eutical interventi­on we can do to mitigate the spread of this disease,” Newsom said.

California has updated its guidance to allow vaccinated people to gather together maskless, as the Centers for Disease Control and Prevention has advised.

“I would follow CDC recommenda­tions, as unified messaging is crucial,” said Dr. Michele Barry, senior associate dean for global health at Stanford University. “Lack of such messaging is what I think magnified the COVID19 pandemic and incurred vaccine distrust.”

Gandhi, however, believes that doing away with the mask mandate “follows the evolving data on COVID. It increases confidence in public health, and it engenders confidence in the messengers. It shows people that we are making datadriven decisions.”

Dr. Susan Philip, health officer for San Francisco, said she’s aware of infectious disease experts such as Gandhi suggesting masks may no longer be necessary outside.

“And we are heading toward a place where we can think about that,” Philip said. “But that’s not the step we’re at right now as a city.”

Others note the broader picture beyond the state. Even though California is doing well with low case counts and hospitaliz­ations, spikes elsewhere could quickly change the picture, as “the virus doesn’t respect state borders,” said Swartzberg, of UC Berkeley.

“I would err on that side that there still be a mandate for the outside until some of these (vaccinatio­n) figures get closer to what we might consider to be herd immunity,” said Stephen Shortell, former dean of the UC Berkeley School of Public Health. “We’re not quite where we need to be.”

The risks outweigh the benefits, particular­ly as we enter a period when vaccinated people may be relaxing other protective behaviors around the unvaccinat­ed, he said.

“It’s so easy to wear a mask,” Swartzberg said. “There’s no harm from wearing a mask, but there are potential advantages to your health and other people’s health.”

One compromise could be carrying a mask for the potential encounter with a large crowd or other high risk situation, like the vocal protest that Shortell said came near his house in Berkeley recently.

“Wearing masks is contingent upon where you are outdoors and how many people are around,” said Barry, with Stanford global health.

Swartzberg said he will reconsider his position when the U.S. has fewer than 10,000 active cases.

Gandhi worries that public health leaders will lose their sway with the public if they wait much longer.

“What are our metrics in a country that is not all on board with masking and distancing forever?” she said. “I don’t want us to have a public health response like this to another pandemic, where half the country is yelling at the CDC director. The data is there.”

 ?? Stephen Lam / The Chronicle ?? Outdoor Yoga SF instructor Kirin Power (left) leads a class of masked students at Crissy Field in San Francisco.
Stephen Lam / The Chronicle Outdoor Yoga SF instructor Kirin Power (left) leads a class of masked students at Crissy Field in San Francisco.
 ?? Santiago Mejia / The Chronicle ?? Fans watch the Oakland Athletics and Minnesota Twins at RingCentra­l Coliseum in Oakland on Tuesday.
Santiago Mejia / The Chronicle Fans watch the Oakland Athletics and Minnesota Twins at RingCentra­l Coliseum in Oakland on Tuesday.
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