But first, let's focus on schools. Lots of various school districts are voting on their reopening plans this week, and they may be reading about a few cases from abroad that may raise concerns here, at least give them something to think about. So joining us is mask expert and University of San Francisco data scientist, Jeremy Howard.

Good to see you again, Jeremy. - Hi there. - All right, let's start with the headlines from internationally. I know you're watching stories out of several different countries. Take us through some of the examples and what they mean for us here. - Sure. The question about the impact of schools on COVID-19 transmission is super complicated.

We don't really know what's going on. Here's the problem. The problem is that normally we figure out what's happening with transmission using contact tracing, which is where we say to people, "Hey, who did you talk to?" And then we go and, you know, "Who did you hang out with?" And we go and see if they have COVID-19.

Problem is, kids almost never get significant enough symptoms that they end up as a recorded case. So there's a huge amount of unrecorded transmission in kids. And we can see that, for example, in Sweden. In Sweden, they did not close down the school system. And then they did what's called a seroprevalence survey, which is where they went around to lots and lots of people at random and tested them.

And it turned out kids had about as much COVID-19 as adults did. So it turned out the transmission was just as bad. We have no reason to believe that those kids can't then go on to pass it on to their teachers and their parents and their grandparents just as easily as adults.

So what we've now seen is, for example, in Israel, they had nearly wiped out the virus. They were down to 10 cases. They opened up schools, and then suddenly it's gone out of control. They're now growing, it looks like, faster than the U.S. - I think yesterday they recorded a thousand cases in 24 hours, right?

So they ordered strict lockdowns again. But what happened and what did it have to do with schools? - Yeah, so what happened was Israel did a lot of things right. They had mandatory masks from early on. They did a lockdown of schools and other things. And then they kind of gradually brought schools back in a very safe way, small classes that didn't interact at all.

They did it for two weeks. And then against the guidance of the health experts, the government said, "All right, everything's open." And it just was bang, everything opened up. And then suddenly within a month, massive outbreaks, we've seen the same thing in my hometown of Melbourne in Australia, nearly eliminated the virus.

Schools opened and now the biggest outbreak in the whole country in a school over, I think it's about 150 people. It's a real worry what we're seeing in the recent weeks is it seems like schools can be a real transmission source. - Well, are they looking at what is going on in those schools?

I mean, are the kids wearing their masks or are they defying orders? Are they not able to socially distance? Have they kind of done a deep dive into what happened? - No time for a deep dive yet. What we do know, for example, is in the Melbourne, Australia case, the school focused a lot on kind of sanitation, hand hygiene, cleaning of classrooms.

They didn't have masks. Reporting that social distancing was poor. Reporting in Israel that masks were not being widely used in schools. So it seems like this respiratory virus, you know, is in a great situation to transfer through breathing, through speaking, maybe even coughing in this indoor environment where there's lots of talking going on.

- Now each school district, as you know, here in California gets to make its own decision. What do you make of Orange County's Board of Education last night voting on their reopening plan that does not actually mandate kids wear a mask while on campus? If they were to consult you, what would you say?

- I would say this is a real worry. Look, kids can wear masks. My four-year-old daughter refuses not to wear a mask. She sees all the adults around her wearing a mask. She sees all her friends wearing a mask. She has a fun, cool mask. Kids can wear masks, it's fine.

And at school, it's really hard to have them distancing all the time, you know, kids will be kids. So we know that when you wear a mask, it means that that droplet cloud, that germ cloud is smaller and distancing works better. So it's gonna make our schools much more likely to be able to open faster and better and more safely if the children are wearing masks.

- But what do you make of the argument that we've heard from some that with really young kids, they could wear it in an unsafe way, leading to more touching and more transmission, and then separately, the social, emotional issues, right? Not being able to read cues when they can't see all the facial expressions due to mask wearing.

And maybe they would get frightened. What do you make of those arguments? - So the first one, I think it's nonsense. We've heard it for adults as well. We're told that people are not capable of wearing a mask. We're capable of wearing all these other pieces of clothing. You know, we can wear socks, we can wear underpants, we can wear masks.

And even if we do it wrong, at least there's something covering our face. Even if we touch it, it's a lot better than touching our face with no mask. As for the learning, yeah, I mean, I don't know what to say. It really is a compromise. It really is tough.

I don't know what the right answer is with schools. But here's the thing. We do know that if we have big outbreaks in schools, they're gonna close down and there's gonna be no learning. And there's gonna be no childcare, and there's gonna be no jobs for the teachers. So in the end, I think we do have to think about what compromises we're willing to make to give our kids a chance to learn.

- I think a lot of people have also questioned the efficacy of masks, right? I read a headline today. I think the director for the Center for AIDS Research at UCSF today said, "Even if you become infected, "masking can still protect you from more severe disease." Can you explain that one?

- Yeah, exactly. So what we've seen in the populations that are wearing masks, which is the vast majority of the world, it's required now, over 80% of the population and over 70% of the U.S. population has to wear masks legally in public spaces. And what we see is not only do the number of cases drop, but it seems the number of deaths drops even faster and even more.

And we think that the reason for that is that the viral dose is decreased. Less of those virions get through the mask and therefore less of them infect you. And when you have a lower viral dose, a lot of virologists believe that that actually results in less severe symptoms and therefore less fatalities and less significant transmission.

So wearing a mask is probably a good idea from both directions. - Got it. Yeah, because you always hear, "Oh, you're wearing it to protect the other person, right? To protect others." But this is suggesting that it could have some effect in protecting you as well. - Yeah, but it depends a lot on what you're using.

You know, there is an increasing availability of kind of surgical masks and better quality masks. And these do provide a better protection to the wearer. - All right, well, I do wanna ask you, there's something cultural about wearing masks here, but President Trump recently wore one in public for the very first time while visiting Walter Reed.

And today CDC director, Dr. Robert Redfield said the key to opening schools is masks, saying the data is really clear, they work. So do you think attitudes have changed and significantly in just the last couple of weeks? - Very significantly. Unfortunately, the thing that's made it change is the big outbreaks in states like Texas and Florida.

It's kind of brought it home that this is a real virus. It's causing real risks and real deaths. And so this awareness that everybody can be hit by this virus, every place can be hit by this virus. So for example, in Texas, Governor Abbott is now requiring masks everywhere where there's a significant number of cases, more than like 20.

And yeah, Donald Trump, you know, when there was an outbreak in the White House, he required everybody in the White House to wear them. And he's now, thank God, being a role model himself and being seen wearing a mask. And I think that's gonna make a huge difference. - All right, and as people start to wear masks more, and actually still debate whether or not they should, there have been lots of confrontations on the streets among strangers, right?

Over people saying, hey, wear yours. No, I don't wanna wear mine. Or people saying, you should be wearing one. And people saying, I don't need to wear one right now. I'm not near people. Can you tell us the scenarios when masks are needed so that people know, so they don't need to confront each other?

- Yeah, I mean, look, I don't confront people about masks. You know, we've got better things to do. It's more likely to cause danger than doing nothing, I think, right? So I'd like to start off by saying, don't be the police. Also, if you see somebody with like not over their nose, don't worry too much.

That doesn't really reduce the effectiveness for protecting you anyway. But given all that, you know, where do you need a mask? You need them indoors when you're around people that you don't see all the time. So not your family or roommates or whatever. And particularly if you're closer than six feet.

Even outdoors, if it's like, if there's no wind, if you're gonna be close to somebody for more than about 15 minutes, I would say that's a risky situation too. Now, of course, in the Bay Area, we have to wear them outside anyway. I think 30 feet is the limit.

For me, I think that's kind of overkill. From a practical point of view, you know, I would say I'd really focus on those indoor public spaces, public transport, shops, stuff like that. - I know 30 feet is San Francisco. Not sure about the other counties, but what if you're just walking out there in the neighborhoods on wide streets and you know to avoid each other, kind of get over to the other side of the street when you see someone coming and you're just kind of jogging by yourself.

Do you need to wear a mask for that? - Not really, I would say don't worry about it. Look, some people are more cautious than others and they might want to put a mask on in that situation, but I don't really think that's important. The transmission rates outdoors 20 times lower than indoors and transmission occurs when you're close to somebody for a period of time and there's a chance for that germ cloud to form.

That's not gonna happen when you walk past somebody unless they like sneeze at you or something, which that would be bad. So maybe that's the one reason. - Well, this is not coming at you, but a viewer wants to know what if you're walking behind somebody who is not wearing a mask?

- Yeah, it's possible. It's pretty speculative. I haven't seen examples, documented cases where that's led to transmission. Doesn't mean it's not possible. I would certainly be a little more cautious myself in that situation. I try not to walk straight behind people across the road or pass them or leave a bit of a gap.

- All right, Jeremy Howard, always great talking to you. Thank you so much for that information. Take good care and we'll see you again soon. - My pleasure. - All right, folks, when we come back, we'll talk with Marin County's health officer about the impact of Governor Newsom's new order to close businesses back down.

Be right back. All right, folks, it's a Tuesday and already a whirlwind week. As you know, Governor Newsom orders sweeping restrictions once again for most counties in California. And so we're talking about it because one way or another, it is affecting you most likely. And a pleasure to have Jeremy Howard on because he has done a lot of studies on masks, the efficacy of masks, and he's been a proponent of masks for all since March.

And it's not really being heated by a majority of the population until more recently. And sadly, as you heard, the COVID numbers are going up. And so more people are wearing the masks and it is not hopefully too late. If we all try to be as safe as possible, hopefully that allows schools to reopen safely and keep the community transmission numbers down and the local numbers down.

Hey folks, some of our regulars, nice to see you. Nice to see you. Lots of opinions about whether people should, kids should go back to school. Some people are advocating for distance learning. Other people saying you will not send your kids to school. Other people saying, what about the mental health aspect and you want your kids in school?

Of course, they are all valid concerns. That is the thing. There's not a single right or wrong answer. It's kind of this constant juggling of ever-changing factors, ever-changing situations and numbers. And no matter which way you cut it, there are drawbacks and there are pluses and minuses no matter which decision you take and which path you take.

Same with all these school districts. So, okay, well then that's our plan. Folks, while we wait for Marin County's Health Officer and Eric, how do we say the officer's name? Lane Hendricks? Okay, they'll be joining shortly. In the meantime, we'll continue to talk with Jeremy. Oh, okay. All right, we are back with Jeremy Howard of Masks for All and a USF data scientist talking about the importance of masking.

I'd like to ask you if you have any more data with regard to the efficacy. And I think for the people who are mostly in the Bay Area are pretty convinced about wearing masks, but in case they're sitting there, not sure, any other data that's new to offer. Yeah, plenty.

In fact, just this morning, I gave a presentation to the World Health Organization on this, so I am full of data, I can talk for hours. Great, good timing. Yeah, some of the most interesting data is what they call ecological data, which is looking around the world at saying, let's look at the places that have put in mask requirements, what happened before, what happened afterwards.

Goldman Sachs actually did a really great study of that. They estimated that if the rest of the country introduced mask mandates, it would add a trillion dollars to the US GDP. Another of these, similar studies has estimated that already we've saved 300 to 400,000 cases even before the end of May through these mandates in the US.

So in the US, one of the things we've really seen in the data is that Americans generally are not wearing masks until we tell them you have to. And then once we say you have to, they are. And this is not surprising 'cause the messaging was all over the place for a long time.

And so this is why we now see over 70% of Americans live in places where they actually have to wear a mask. Okay, Jeremy, you also put out something that I thought was very interesting today, which is cleaning solution ingredients that work against coronaviruses. I know a lot of people are interested in this, so tell us what are those ingredients and what should we have in the house?

I do not remember off the top of my head. Hopefully you can dig it up and maybe pop it on the screen. I will run through this with you. Let's see. I'll tell you what though, what I wrote there was like what I got from the Singaporean health body is the underlying chemicals.

So that way you don't have to look at every brand. Thank goodness. I can't say the names of those chemicals anyway. But look on the bottle, right? So if you can put it on the screen or say them, look on the bottle for these particular chemicals because they basically all have the same thing.

And when I looked around our house, we had like somehow we had six different bottles of cleaning fluid and five of them had these chemicals which were effective against coronaviruses. Yeah, but generally what are those products? Accelerated hydrogen peroxide, benzylcholineum chloride, coral, silanol. Yeah, so that's like bleach. Yeah, yeah, it's just like, you know, they're just the chemical names for bleach and stuff like that.

So they're really normal standard kind of things. The other thing I wanted to mention which I've looked at recently is the research around masks for protecting the wearer, not just for protecting others. And there's actually a whole lot of interesting stuff going on there. You can now buy, you know, pieces of kind of special filter paper which are actually designed to protect the wearer.

One I really like, I don't get paid for any of this, it's just stuff I've seen that I've bought is called Filtee, F-I-L-T-I, which is originally this company made like air conditioning filters and then they switched to mask filters and they've actually been tested on the same equipment they use for medical masks and it's actually getting the same level of filtration.

And so if you now go to like Etsy, you can buy from hundreds of different kind of community DIY crafters, masks with these Filtee pockets which are gonna do a fantastic job of protecting you as well as the people around you. - Oh, I do see a lot of that, Filtee fabric.

All right, thank you so much. You always have interesting advice for us and we appreciate it.