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“Any mandate we’re looking at would be temporary, this is not a forever thing,” BART District 8 Director Janice Li told SFGATE. “Our policy needs to be data-driven. When the TSA extended the mandate for an additional two weeks, it gave us some runway see what cases look like with BA.2, and we’re seeing an early uptick in cases again in the region.”

But is it possible the BART mask mandate — and transit mask mandates generally — have minimal impact on the spread of the virus? Studies on mask-wearing show that the strongest protection comes from wearing well-fitted high quality masks such as N95s and KN95s. Cloth masks and surgical masks have been shown by two separate studies to provide minimal protection against even the early strains of the virus, to say nothing of the more contagious delta and omicron variants.

Individuals who would go maskless in the absence of a mandate might wear cloth or surgical masks if a mandate were reimplemented. Individuals who are wearing N95s and KN95s with a mandate may continue wearing those masks even without a mandate. So are transit masking policies actually doing anything?

Li said that because she’s not an infectious disease expert, she did not want to speculate. SFGATE reached out to two prominent UCSF COVID-19 experts — Dr. Bob Wachter and Dr. Jeanne Noble — to get their insights. Both agreed that high quality masking provides substantial protection to the wearer — even if they’re interacting with maskless individuals known to be COVID-19-positive.

“Wearing an N95 or equivalent provides excellent protection,” Wachter wrote in an email. “It’s what we wear in the hospital when we’re taking care of patients we know have covid! And infection from patient to clinician is very rare. Low quality cloth masks provide next-to-no protection and should not be counted on.”

“The use of low quality (cloth) masks is not likely to make any measurable difference in viral transmission so it doesn’t matter whether you or others are wearing one,” Noble wrote. “One way masking with an N95 is the form of protection used and accepted by health care workers on a daily basis – our sick respiratory patients breathing hard and fast because they are sick with COVID or influenza or TB are unmasked and we are up close taking care of them (<6ft for >15 minutes) on a regular basis. We are considered protected because of 1 way masking – my N95 protects me and I do not worry about my patient with a heavy viral load not being masked.”

Noble said studies on masking lead her to believe that mask mandates — whether on public transit or elsewhere — have scant impact on the spread of the virus.

“Our single positive randomized controlled trial for masks done in Bangladesh found no protection for cloth masks, and a ‘relative risk reduction’ of 10% for surgical masks only for persons over age 50 which translated to a <1% absolute reduction in getting symptomatic COVID for this age group,” she wrote. “Given this very modest benefit even for surgical masks (reducing transmission by 1% or less), mask mandates may create a false sense of reassurance to those who truly need the extra protection.

“The severely immunocompromised person (eg., organ transplant, on B cell depleting therapy, aggressive chemo) 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.”

Wachter disagreed with Noble on this point, stating that he believes the absence of mask mandates will be “part of a general decrease in caution,” causing an uptick in transmission.

“It’ll be hard to separate the impact of travel-related spread from spread in other places where people are no longer masking, from the new subvariants, which are more infectious than the original Omicron,” he wrote. “And yes, if it’s no masks vs. people wearing cloth masks, the difference would be real but not huge, but you had a mix of people wearing different quality masks, so the effect is a blend of the loss of all that protection.”

The two experts also agreed that planes are lower-risk environments than buses and trains because of better ventilation, and Li, Wachter and Noble noted that BART typically has very good ventilation.

Noble also argued that “there is nothing special about buses or trains versus restaurants/bars/large indoor entertainment venues,” and that “blanket mandates for ‘masks while on buses or trains’ just isn’t scientific.”

“I think the average citizen senses the inconsistency here (not dissimilar to our previous decision to drop mask mandates in schools later than all other public spaces),” she wrote. “This inconsistency undermines public trust in public health officials. Mandates should be consistent, effective, and necessary. Isolated public transportation mask mandates fail on all 3 counts.”