UCSF’s Dr. Bob Wachter explains why he’s masking up again

COVID-19 cases are rising in California and UCSF’s Dr. Bob Wachter posted on Twitter Monday that he reverts to more cautious behavior and puts his mask back on in indoor public spaces where they may not be needed.

“Last month SF got a lot less masked,” Wachter wrote on Twitter. “At this point, if you’ve decided you’re okay with getting Covid (which isn’t crazy if vaxxed/boosted), then it’s fine to keep the mask on in crowded indoor spaces. If you prefer avoid Covid and have become less cautious, it’s time to rethink.”

Wachter said he was covering his face again because he preferred to avoid COVID. He said he was mostly worried about the long symptoms of COVID and the long-term risks, including heart damage, neurological impacts and diabetes.

“I will now do 100% N95 in crowded indoor spaces,” Wachter wrote. “I will strongly favor eating out rather than indoors, but I will eat indoors in small groups (acknowledging it’s a risk, but worth it). You should do your own choice, but do it with your eyes open: there’s a lot of Covid out there.”

Wachter is the chair of UCSF’s Department of Medicine and has been tweeting about COVID-19 for more than two years, sharing regular updates with his perspective on the state of the pandemic in San Francisco and around the world.


After peaking in January amid the omicron surge, San Francisco saw a significant drop in cases and the city relaxed the health mandate, no longer requiring masking in most indoor public spaces. Cases are rising, though it’s unclear to what extent state and city data is less reliable, as there are fewer testing sites and more people testing from home. Wachter said the rate of asymptomatic positive tests at UCSF, where patients must get tested before certain procedures or if staying overnight, is a good indicator of community prevalence. He said in the past week the rate has tripled to 3.4%, meaning one in 30 people in San Francisco is asymptomatic.

“I had slipped a bit on masking in non-crowded spaces and was less cautious on restaurants,” Wachter said. “I’m resuming a more cautious behavior.”

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