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Wearing a masking to protect yourself and others against the spread of the coronavirus has become something of a political, social, and emotional fireball. Should the vaccinated continue to wear them? Is a mask really necessary outdoors? So many questions remain, but the answers are hard to come by as health agencies, local officials, and even health experts seem to continually change their recommendations.

On this week’s episode, Monica Gandhi, MD, MPH, associate chief in the Division of HIV, Infectious Diseases, and Global Medicine at the University of California San Francisco, joins us to help break down what the science shows about masks and their ability to protect us.

The following is an abridged transcript of her interview with “Track the Vax” host Serena Marshall:

Serena Marshall: Dr. Gandhi, thank you so much for joining us.

Monica Gandhi, MD, MPH: Thank you.

Marshall: So masking, really, it’s become something of a flashpoint. I think … maybe catching a lot of public health officials by surprise?

Gandhi: Yes. I mean, actually I have to blame some of our messaging on masking as well. And why it is such a political issue and why it’s not explained well and, you know, sort of going back — thinking about what happened April 3rd, 2020. The CDC said everyone should universally mask because there’s asymptomatic transmission with this virus.

Even if you feel well, you can pass it on, but there was no distinction in the type of mask if that protected you as an individual. And that messaging stayed intact for a long time, and then they changed it and said it protected you and others on November 9th.

Marshall: But I think that the confusion isn’t just public health officials to the general public, it seems sometimes it’s a little bit confusing even within public health circles. What do we actually know about masking protecting people?

Gandhi: Yes. I mean, that’s exactly it. We didn’t have good science on masks before this pandemic. We just sort of …

Marshall: So, Dr. Gandhi, that is so surprising.

Gandhi: Yeah, yeah. I mean, to be fair, we didn’t. So, number 1, we kind of knew, and it’s again, more vague that if you have tiny particles, which would be more like aerosolized pathogens like tuberculosis, that you need a mask, that fits really tightly on your face, like an N-95 and is really tightly woven.

But actually, even that science isn’t completely worked out, because when you look back in the literature, even a surgical mask that we’re all running around wearing right now, has some protection against tuberculosis, which is aerosolized. And then we didn’t have good masking data or big studies on droplets and what will block a droplet, and so a lot of our masking studies came out of this pandemic, but no, we didn’t have good masking studies before this pandemic.

Marshall: I want to back things up just a second here. Why did doctors wear masks in surgeries?

Gandhi: It was actually more to, you know, you don’t want to spit into a surgical field. I mean, it’s that simple. Like you could … everything about the surgical field is about cleanliness and about sterility … you absolutely, when you’re talking, can have stuff come out of your mouth — spit and so forth. You just, you can’t have the field, it’s disrupted like that.

Marshall: Not so much about the spread of disease, but just about human sanitation.

Gandhi: Exactly — sanitary conditions in a surgical space. Did we ever have good studies, by the way, on masking surgeons versus not masking surgeons? No. We had good studies on hand-washing and wearing gloves, because that’s what’s in the patient when you’re working, but no, we didn’t have good studies. It just seemed like it was a good thing to do — human sanitation.

Marshall: Okay. So what have we learned about masking and viral spread? You said a lot of the good studies came out of this pandemic. What do they look like, since it has only been … I mean, you say has only… it’s 18 months now. But what do we know?

Gandhi: So, the good studies, and I know that people will quibble with this, but are physical science studies. And I’ll say why people quibble. But these are studies where you put a type of material on a mannequin, and you spray that mannequin with different types of particles of different sizes. Like that looked like aerosols and droplets, and you see how much gets in and how much gets out depending on the fit on the mannequin.

Marshall: So that’s like the DOD [Department of Defense] study that we saw back, end of last year.

Gandhi: Yes. And these are physical science experiments. And the reason that I sort of say it a little bit, like, you know, the doubt question that comes into people’s minds, I got a lot of people who write to me because they’re angry about masks. And they will say, you know, our hopes and prayers for the mannequins …

And what they mean by that is that they want randomized patient studies on masks. But the point is with a physical barrier … You know, one example is condoms with HIV prevention that we didn’t, we never had a randomized controlled study. It was actually about the physical size of the virus and using a condom for HIV prevention.

And we know that human papillomavirus is too small and it can get through a condom and HIV is too big and it can’t, but it was really around the physical science aspect of these studies.

So there are now good studies that look at physical science and say, if your mask is tight, if your mask is made out this material, if it’s fit, and filtered, it’s going to block more coming … spew going out and more coming in. And those are great, really well-done studies that give us a lot of data on masking.

Marshall: And so break down what we’ve seen from a couple of those studies. And those studies, just to clarify here, are different from, maybe, some of the real life MMWR studies we’ve seen come out of the CDC.

Gandhi: Yes, and we could talk about those too. But going into the physical science studies, there was some great studies. There was one that came out February 9, 2021 — that was the CDC MMWR physical science study, where they really showed this. I also performed a study with Linsey Marr, a physical scientist at Virginia Tech, and we published that in [December 2020] in Med. It involved these mannequin-type studies and using different materials.

So what did it show? Well, polypropylene, which is what surgical masks are made of, has characteristics of them that block virus, which is, it’s this simple: they’re negatively charged. And so is a poly and so is a viral virus, SARS-CoV-2, so that there’s a physical electrostatic repulsion between viruses and polypropylene material. And so that, that is pure and simple how they block.

Marshall: And to put that in a little bit more layman’s terms: It’s basically like two positive sides or two negative sides of a battery repelling each other.

Gandhi: Exactly. So a magnet, and they hate to be around each other if they’re both negative. So that’s exactly right.

Then the polypropylene material’s negatively charged, the virus is negatively charged, and it electrostatically, just repulses that virus. So that’s why polypropylene material is so good.

And it’s kind of this non-woven specific type of material, and we’ve used it in hospitals forever for surgical masks. Then, we looked at a bunch of different cloth materials and frankly, cloth is anywhere from doing nothing. If you have a gaiter or something that’s really loosely fitting and it has really big holes in it, they don’t block virus at all; if you have really tightly woven cloth material, they’ll block more virus and also double layered.

And so of all the mass combinations or the types of masks that we found block virus the most, one is N-95, which we didn’t even bother studying because that was studied a lot.

Second is those KN-95s are good in terms of blocking, because it’s made out of that material, and they’re also tight-fitting.

Third is surgical plus cloth together because the surgical is blocking it like an electrostatic charge. And the cloth is like a bumper course. The virus tried to come in and it keeps on hitting different parts of the material and it gives up.

And then the last one is those cloth masks, but you put a filter paper inside of it, and that’s still trying to do that combination of polypropylene and cloth. That’s probably the thinnest option that you can get. Those ones you can buy on Amazon, you put filter paper inside, and those are the four masks we liked.

Marshall: Okay, so if I go on Amazon and order a double-layer cotton mask, that’s really not doing much for me?

Gandhi: It’s not doing … it’s doing some, like, there’s blockage depending on how good the quality of the material is between 52% and 65%. And there’s a bunch of different mask studies that show that, but it’s not 95%, which is what you’ll get with a surgical plus cloth, or you’ll get with a cloth and then sticking that filter material inside of it.

Marshall: Okay. But there’s still concerns about PPE [personal protective equipment] availability. So sometimes getting those surgical masks might be difficult, especially if folks start stockpiling them again. So I feel like people are still going to be confused on what they’re supposed to do. I mean, especially add in the layer of vaccination, right? So you’re vaccinated, why do you still wear a mask, especially if your mask is made of cloth and you don’t have a N-95?

Gandhi: Yeah, exactly. I mean, just to just make one point clear: N-95 is different than what I mean by a surgical mask, because the N-95, we actually use the word “respirator” in medicine. But it’s that super tight-fitting one that we actually fit test people and make sure they can’t smell anything.

And then a surgical mask as those pink and blue ones that are out there. I bought pink recently. They’re out there and you’re just seeing people wear in the store. Those are good masks, surgical masks.

But yes, it’s so true that as we’re talking, you can see all the confusion because some masks were better than others.

And then, now, we have vaccination in the mix, right. And vaccination, no matter what, and I will never, ever, even listen to someone who says a vaccine doesn’t work better than a mask. Vaccines are working extremely well. And I just think that we ended up, you know, kind of … in this country, not in other countries, we kind of brought down the effectiveness of the vaccines by our messaging when the CDC put back masks.

So when they put back masks on July 27th, they didn’t mean to say that you’re equally likely to spread infection if you’re vaccinated and you got a breakthrough than if you’re unvaccinated. They said that for a couple of days, but then they actually changed their tune. And that’s because there was more data.

And a Singapore study showed us that for one point in time, you may, and you don’t feel well because you have a vaccine breakthrough. You may have a lot of virus in your nose, but your virus comes down very quickly, because that’s what your immune system does, is it hurts it and it makes it come down. And then another Netherlands study showed that you don’t culture very well.

Meaning the virus doesn’t culture out very well. It doesn’t grow very well if you’re vaccinated, because your immune system gets happily to work on that virus and it hurts it and it kills it. So it brings down its level of infectiousness. So that was confusing messaging by the CDC, unfortunately, I think.

It was probably part … we probably shouldn’t have taken masks off just for the vaccinated and not the unvaccinated because no other country did that. We should have just lifted them when we’re at a certain level of circulating virus, but it was too much back and forth and that confused a lot of people.

Marshall: But, so where does the “forth” stand then, if you’re going back and forth? Do vaccinated people need to wear a mask? And what’s the reason behind it?

Gandhi: So, this is how we think about a vaccinated person: If you’re in an area of high circulating virus, these vaccines are great, amazing, at protecting you from severe disease. But it can’t protect you from your antibodies taking a little while to kick in to fight it. And you may get a mild breakthrough if you’re in an area of high circulating virus.

And the estimates are in the United States we’re now at something like 1-in-20,000 in San Francisco, because we have low circulating virus. And 1-in-5,000 in places in the United States of getting a breakthrough infection.

So the reason to wear a mask after vaccination is because we didn’t control transmission because we didn’t have the rates of vaccination that other developed countries did, period. We didn’t have the uptake. When virus is running around, you can get a cold, you can get a flu, and you don’t want to get that. So that’s the reason to wear a mask in areas of high circulating virus.

Marshall: But Dr. Gandhi, is that just to protect yourself then from getting that breakthrough, is it to protect others like those children who don’t yet qualify for vaccines, or even those who choose not to get vaccinated?

Gandhi: So great, so it’s both. So, what I just said is true, that it will protect you from mild breakthroughs. But, what about the question of protecting others? Well, this is, I think, where that messaging is very confusing. You do have an immune response when you get vaccinated. But what the Delta variant showed us is that if you have a symptomatic breakthrough, that you can spread it. And that’s different than when people had a symptomatic breakthrough with Alpha.

Meaning, we actually saw that the virus, you couldn’t culture out at all. But it’s true that if you get a breakthrough infection, you can likely spread it. And that means that you’re protecting others in the setting of Delta during this time of having Delta, even if you’re vaccinated.

Now, can you spread it when you’re asymptomatic? The answer to that question is, I don’t know. And I’m not sure you can. Because there was a really strong Singapore study that did very careful contact tracing, and those were asymptomatic and vaccinated, they didn’t see any transmission … even in the time of Delta. So this is what I mean, the data keeps on changing.

There’s a lot of confusing messaging. Right now putting masks back for the vaccinated was indoors when Delta was spreading a lot is helpful, both for the vaccinated, and if you don’t feel well, but you don’t realize that you’re getting a breakthrough, you could spread it. So that’s probably the right thing for unvaccinated people around you.

But the reason that we are so up in arms about masks is even the way I’ve explained it to you still led to a lot of confusion.

Marshall: Yeah. I mean, honestly, I’m still wondering, like, do I need to wear it when I go outside or to an indoor workout class? Does my daughter need to wear it when she’s on the playground? And a lot of her masks, you know, come from a store up the street and … it’s not a cloth mask. I don’t even know if I found a cloth mask that will fit her face.

Gandhi: Yes. So that’s, it’s very important to talk about. So outdoor transmission, how rare is it? It’s rare. It’s that data isn’t changing. And by the way, when we say: “Oh, but we don’t have data in the time of Delta,” Delta has been out since March 4. That’s actually when the cases started coming up in India, and that was the first place this Delta variant was discovered. No, we have quite a bit of data on Delta, now as we’re getting into October. So we have data on Delta.

Outdoor transmission for this virus, whether it’s Delta or not, is very rare, because it just doesn’t like ventilation. It doesn’t like the outside air, and it dissipates quickly in the outside air. And so because of that, outdoor masking, no one is actually really recommending strongly. And you will see people outdoor masking and it’ll be more, maybe, aligned with politics, but there isn’t … there really isn’t biological data that says you have to outdoor mask. And so that includes a little child on a playground.

And then let’s go to the question of children, because that’s important. The reason that’s so important is children get less severe disease. They’re less likely to get infected because it’s just a receptor issue. Especially as small children, they have fewer of the receptors that are in their nose to even get in the virus.

So the WHO says don’t mask under age 5 and the CDC says don’t mask under 2. And even that difference alone has caused so much distrust because we don’t know if you need to mask between 3 and 5. That was sort of based on the CDC’s decision that “let’s just be overcautious,” and the WHO is representing the entire planet.

And they’re looking at the receptor data and they’re saying: I don’t think less than 5 gets sick very much so, and they also have to learn how to talk. And so there is a lot there that has caused distrust about whether we should be masking toddlers or not.

Marshall: I’m glad you mentioned that: have to learn how to talk. That’s an argument I’ve seen a lot on social media that when it comes to kids, they’re still at a very vulnerable age of growth. Seeing facial expressions matter and it’s vital to cognitive development. So, how do you navigate this world of masking with parents?

Gandhi: Yes. I mean, I would say that you have half of parents who truly distrust the CDC for making it to 2 when the WHO has made it 5. And then you have the other half of parents who are: “well, we can never be too careful.”

And this is the problem, that unless you have good data on something, you are, if you do make a declarative statement, you are going to be distrusted.

And so what do we have good data on? Vaccines work. Masking — this mask is a better mask than this mask. The mask that we just talked about indoors. And that … we also finally have good data that in general, and this is kind of ecologic data, but places that mask and had a high compliance with masking did better than places that didn’t. Those were pretty much the extent of our data.

We don’t have great randomized controlled data, which we can talk about if we have time. But, if you make declarative statements that a 3-year-old in the United States has to mask, but nowhere else in the world has to mask, you will create distrust. And that is frankly what we’ve done with the 2- and 5-year-olds because it is a delicate time of growth and cognitive development and seeing faces and seeing smiles and all of that means something.

Marshall: So I want to mention, you just mentioned large randomized trials and studies. With adults, I believe, there is now the largest randomized study, 340,000 participants in a Bangladesh study. So I wanted to dive into that a little bit, because when we have your study that we talked about a minute ago, which looks at the type of masks and how the virus gets repelled by certain masks, this study seemed to show a 9.3% reduction in symptomatic COVID seroprevalence.

Now, that doesn’t just mean that it was only a reduction of 9%, for those who masked?

Gandhi: Right, so importantly, it was a cluster randomized trial. So this is like randomizing neighborhoods, you know, essentially villages in this case, to surgical mask, cloth masks, and also interventions designed to increase mask wearing.

And above 50 there was a reduction in symptomatic disease. And yes, it was small though that we don’t know if we’re catching all symptoms. It was about 10%.

And then seroprevalence is if you had a serious enough infection to actually seroconvert, because importantly you could have a mild infection and not raise very strong antibodies depending on when you measure them. So it’s kind of a weak surrogate for exactly understanding transmission, but it’s the best we’ve got probably.

And it does show an effect. I mean, to tout it as showing like, you know, this is the definitive answer, no matter what, masks work … is also an over exaggeration. But that’s because I think that randomized controlled trials aren’t always the best way to study — whether they’re cluster or individual level — aren’t the best way to study interventions where it involves human behavior. Because of human behavior, we don’t know what people are doing inside.

It is hard for little kids to keep it up above the nose and mouth. It depends on the age of the population who is even going to get disease, because younger people are less likely to get disease. So it’s still imperfect.

Randomized controlled studies of masks are imperfect, but yes, in general, it didn’t show an effect of cloth masks. It showed an effect of surgical masks — that’s that polypropylene-repelling electrostatic charge material. And it was reduced symptomatic disease in those who were most susceptible to symptomatic disease over 50.

Marshall: Okay. So it’s just another check mark on the board for returning all of my cloth masks and ordering some new surgical ones.

Gandhi: That’s what I did. I mean, I’m not kidding actually. Right after that I actually did that. I hate blue. I don’t know why. I liked the color pink. So I ordered surgical masks and I started only surgically masking in stores after that. Because though I think that cloth masks, depending on their cloth, what we talked about before, depending on the type, may have effectiveness, there’s just truly something biological about that material, that repels virus. That surgical mask that you’d see in the movies of people, not the really strong one, but the pink and blue ones. And so, yeah, I would, I would go for a surgical mask after this.

Marshall: Can you wear those more than once, Dr. Gandhi, or are those where once into the grocery store and toss them after?

Gandhi: No, I’m very worried about the environmental impact of all this masking, actually. And I didn’t love that study, that it showed a better effective surgical mask. Cause I really liked the idea of washing.

I wear them for 3 days. I have like a whole system going on and especially since I’m only wearing them sporadically, except if I’m at work. The pink ones, what I wear for clothes, for inside stores and what not, I will mark it out and I’ll wear it for 3 days

Marshall: Three days. And if after 3 days, then you toss it.

Gandhi: Yes. Importantly, they also repel water. So they’re less likely to get wet, which is a good thing. So they are really quite durable.

Marshall: Okay, well, what about leaving it in your car or in your bag, your work bag?

Gandhi: I leave it in my car, but not where it can see the sun. So I leave it in my car, in the glove compartment. Because the sun can break down that material. So I just leave it in the glove compartment and I keep them clean and I wear them for 3 days.

Marshall: Okay. What about wearing makeup with them? Will that break down the middle?

Gandhi: No, and I do wear makeup, but I really hate how lipsticky and gross it looks on one side. So I’ve just sadly given up on makeup during this time, or at least lipstick. But, it won’t break it down. It’ll just make it look messy.

Marshall: Are there other tips people should be aware of when utilizing these masks?

Gandhi: Yes. I mean, the one thing that we showed in our physical science study is it’s not just the material of the surgical mask that’s better, but it is. The other is the fit. So make sure that it fits and it’s not baggy. And what you can do if you have a small face is double loop the side, so when it goes over your ear, do a crisscross on each side, so it fits.

Marshall: Great. And I think the biggest question Dr. Gandhi, and one we’ll end on is what’s it going to take for us to be able to toss those masks for good?

Gandhi: Well, I will say that I fundamentally believe that we should. Meaning anyone can mask if they’d like to, to prevent a cold and influenza in the future, because we didn’t see a lot of colds, we didn’t see a lot of influenza. And I think that it’s likely that it was the social distancing and the masking that did that.

But mandating masks for more mild infections is not something that’s going to fly in a country, and I also — and this is a longer topic — but I do think we need exposure to mild pathogens in the future for mean diversity. So there should be metrics. There should be metrics for when we can toss masks …

And the reason that there should be metrics is we just spent this last half an hour talking about trust and the data being in and out. And some of the data not being clear in different public health places, saying different things. And the cleaner we are, when we tell the public that they should mask and unmask, in terms of objective metrics, the more trust we will generate.

So the CDC had previously said it was vaccinated, and then they took that away. And, I think that’s fine, actually. They took it away, but then that means they need metrics of when we can unmask. They did actually put in metrics in a way. In the CDC MMWR article from June 30th, they said in the rates of vaccination, you can take off your mask when you’re vaccinated, when you have low or moderate transmission in the region.

And they defined that in two ways. They defined one as a low test positivity rate — 5% for many campuses; many cities are already below 5%. We’ve been below 5% in San Francisco for about a month. And then the second is they, and this was a more confusing metric: 10 over 100,000 cases, cumulatively — like 10, basically per day, over 100,000 people.

And the problem with that is that it matters how much you’re testing. You may be testing only asymptomatic people who are not likely to have it, and you may be testing, or in one city only testing people’s symptoms. So that one is a little bit harder.

And I think test positivity is a good one. I personally had my own metric, which was hospitalization rates in a region. That if you were down to 5-10 over 100,000, that vaccinated people don’t need a mask. So even on vaccinated, because that means you have low rates of transmission. Whatever we come up with, there should be clean metrics that tell people they don’t have to mask.

Marshall: Dr. Gandhi, thank you so much for joining us.