Do mask mandates work? Bay Area COVID data from June says no.

Photo of Eric Ting
A sign in a business window along Chestnut Street reminds customers to wear face masks while indoor their store in San Francisco on Jan. 4, 2022.

A sign in a business window along Chestnut Street reminds customers to wear face masks while indoor their store in San Francisco on Jan. 4, 2022.

Douglas Zimmerman/SFGATE

In early June, during an uptick in COVID-19 cases, Alameda County was the only Bay Area county to bring back an indoor mask mandate.

At the time, county Health Officer Dr. Nicholas Moss said, “Putting our masks back on gives us the best opportunity to limit the impact of a prolonged wave on our communities.”

But regional case data provides no discernible evidence that the rule, which was lifted June 25, succeeded at that goal.

The graphs below compare Alameda County’s seven-day average case rate from the past two months to rates in neighboring Contra Costa, Santa Clara and San Francisco counties. Contra Costa and Santa Clara, in particular, are natural comparisons to Alameda, because they have similar vaccination rates and demographic data. San Francisco, on the other side of the bay, provides an additional point of reference. All data comes from the California Department of Public Health.

The case rate curves for Alameda and Contra Costa counties are near-identical. Because the neighboring counties are similar in so many respects, if masking policy had an impact on pandemic outcomes, one would expect to see some sort of discrepancy in the graph.

San Francisco and Santa Clara had higher case rates than Alameda County throughout the current surge, including pre-mask mandate. Once the mandate was introduced, the three counties all followed the same trend line, casting doubt on whether the mask mandate did anything to curb transmission at the community level.

SFGATE sent Moss these graphs via email and asked whether he can point to any evidence that his county’s mandate had an impact on reducing caseloads. 

“We believe the recent mask order contributed to the improvements we are now observing with COVID-19 in Alameda County,” Moss said in a statement. “Conditions are more stable now than at the time the Order was put in place.”

“Published evidence shows that high levels of community masking lowers transmission rates and survey data displayed an increase in masking during the recent Order timeframe,” he added. “In fact, Alameda County observed higher masking rates than anywhere else in the Country at the time.”

The Alameda County Health Department did not respond to follow-up questions on how Moss determined his county had higher rates of masking than anywhere else in the country, and how, if that statement were true, the graphs wouldn't cut against the claim that "high levels of community masking lowers transmission rates."

Alameda County’s mandate was implemented not long after the New York Times published an article titled "Why Masks Work, but Mandates Haven't.” The piece states that high-quality, well-fitting masks can help minimize an individual’s risk of catching or spreading COVID-19, but community-level mandates have failed to affect case rates because the virus is so contagious that it spreads easily in the moments when people take their masks off to eat, drink or be comfortable.

After viewing the case rate graphs, UCSF’s Dr. Bob Wachter — one of the region’s more cautious COVID-19 experts and a supporter of mask mandates — echoed many of that article’s sentiments, stating that mandates don’t appear to increase the “probability of people wearing good masks correctly.” Many people find it difficult to wear an N95 for long periods of time, instead opting for lower-quality cloth or surgical masks.

“If the mandate came with enforcement of wearing a good (N95 or equivalent) mask correctly, it might demonstrate a significant advantage in preventing cases,” he wrote to SFGATE in an email. “But there is no real enforcement (certainly not of correct masking using a good mask), which means that the rates of effective masking probably isn’t very different in [the Bay Area counties being compared].”

If, in order to have an impactful mask mandate, enforcement teams must ensure that people are correctly wearing N95s indoors, it seems like a policy doomed to fail whenever implemented. It also raises questions of whether the costs of such enforcement would exceed the benefits.

Residents of the San Francisco Bay Area, with high rates of vaccination and infection-acquired immunity from the past two surges, are well-protected from severe disease and death. Over the past two months, hospitalizations across the Bay Area have come nowhere close to the winter omicron numbers, which may not have accurately reflected the actual impact of the disease on hospitals. Alameda County's hospitalization-per-capita numbers are comparable to Contra Costa's and Santa Clara's.

Wachter has long pointed out that anyone who wants to limit their chance of catching COVID-19 can easily do so by wearing a well-fitting N95 when they go out in public, with or without a mask mandate. It’s rare for physicians to catch the virus while wearing N95 masks, he told SFGATE, even when interacting with patients who have tested positive.

Wachter’s UCSF colleague Dr. Jeanne Noble, too, is a proponent of high-risk individuals protecting themselves through careful mask usage. Mandates, she told SFGATE in April, drive people to wear low-quality masks, which are “not likely to make any measurable difference in viral transmission so it doesn’t matter whether you or others are wearing one.”

“Mask mandates may create a false sense of reassurance to those who truly need the extra protection,” Noble said in April. “The severely immunocompromised person … should be using an N95 in crowded spaces when viral prevalence is high. They should not opt for a cloth or surgical mask because other people around them are masked and therefore assume it is 'safe enough' to avoid the tight fitting and uncomfortable N95.”