'Do What's Right By the Science:' Why the CDC Updated Outdoor Mask Guidance (And When You Can Ditch Yours)

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The CDC has updated its guidance on mask-wearing outside. (Samson Katt/Pexels)

This week, Gov. Gavin Newsom announced California would be moving to align with new guidelines issued by the Centers for Disease Control and Prevention, relaxing the mask mandate for people who are fully vaccinated against COVID-19.

The new guidance from the CDC says that fully vaccinated people don't need to wear a mask outside if they're walking, running or biking, attending small outdoor gatherings or eating outside at a restaurant. Fully vaccinated people now only need to wear a mask in large crowds of strangers, says the CDC.

As for people who aren't yet fully vaccinated, the CDC says they can also be maskless outside with members of their household, or go maskless at a small, outdoor gathering as long as others in attendance are fully vaccinated.

All nine Bay Area counties have said they plan to adopt the new guidelines once California formally aligns with the CDC's new recommendations. On KQED Forum, Priya David Clemens spoke with Dr. Monica Gandhi, infectious disease expert and professor of medicine at UCSF.

KQED’s Priya David Clemens: You have been advocating for reducing mask use for some time now. Could you tell us about your thoughts?

Dr. Monica Gandhi: I do want to stress that I co-wrote one of the first papers in early April 2020 about universal mask use for the American public. I’m definitely very interested in mask use as a mitigation procedure along with ventilation and distancing. However, when you think about ventilation and you think about this virus, there's actually incredibly clear studies about how hard it is to get coronavirus outside.

The most impressive study was published in September from China, where they do very strict contact tracing. And out of 7,324 infections, only one was linked to outdoor transmission.

There was an Irish Times article about a month ago that showed that out of 232,000, one out of a thousand was likely linked to outdoor transmission. And then a very extensive review from the University of Canterbury was done earlier in the fall and looked at a massive number of studies around the planet and thought that outside transmission was so rare that they couldn't actually quantify it.

And then when the World Health Organization revised their mask guidance in December — even before vaccines — they said masks are not required outside unless you're in non-distanced situations. That's some of the evidence even prior to vaccinations.

The CDC's latest guidance for outdoor mask-wearing, for fully vaccinated and vaccinated people. (CDC)

So Dr. Gandhi, what do you do when you're outside? Do you wear a mask?

I did until yesterday, because I'm really very polite — and also because of the San Francisco guidelines, which were actually put into place on April 17, 2020, two months before the state put in place their outdoor and indoor mask mandates.

However, I actually realized yesterday after the CDC released their guidelines that as someone who really is trying to follow the data, and has really deeply looked at these outside studies, it's best for me to model not wearing my mask outside. Yesterday I went without my mask outside, and no one got mad at me.

Don't be frightened to do what's right by the science and take off your mask outside. The more of us that do it, it'll become the new social norm. And we can smile at each other.

What was it like? Did you get some strange looks? Some people may feel you are not being respectful.

San Francisco has been a city that has very been very compliant with mask wearing. We have used this symbol of mask wearing as respect, and that we follow the science.

The issue is that it is following the science to understand how quickly viral particles disperse in the outside air for modeling, and all the epidemiology evidence.

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It's tremendously respectful to science to not wear your mask outside even if you're not vaccinated. And I'm fully vaccinated. Someone gave me a very wide berth when I was walking up to my clinic since I didn't have my mask on outside, but still, I thought it was important to do that.

What about some parts of the city and in various communities outside of San Francisco, where the COVID infection rates have been higher than San Francisco? Are there places you should still wear a mask outdoors? 

The fascinating thing about the science around mask wearing outside is that it's actually delinked from the question of your vaccination status and delinked from the question of case prevalence. As the World Health Organization put in their guidelines in December 2020 — it's about the outside being so much safer.


I think we've actually focused a little bit too much on closing outside playgrounds. For example, in December, we've done things that sometimes can hurt public health when we don't remember how important and safe the outside is. But the recommendation in my mind should be: Don't wear a mask outside, unless you're in packed conditions. And that's where I chose to wear it.

And I would still wear it inside. Not necessarily that you can transmit it after vaccination, but because we're not all vaccinated — and I think that's a sign of respect here.

This interview has been edited for length and clarity.