
As we continue to navigate these unprecedented times, KCBS Radio is getting the answers to your questions about the coronavirus pandemic. Every morning at 9:20 a.m. Monday-Friday we're doing an "Ask An Expert" segment with a focus on a different aspect of this situation each day.
Today we continue to explore how the virus transmits in the community and the recent rise in cases with Dr. Bob Wachter, chair of the Department of Medicine at UC San Francisco.
I want to ask you before we get too deeply into the listener questions for your take on the news out of the United Kingdom today, the very closely watched University of Oxford AstraZeneca vaccine study.It's terrific news as is the news that we got last week from the Moderna vaccine in the United States, they're all seeming to show that the vaccines are leading to antibody responses, as you'd hope, and not leading to significant numbers of side effects, as you'd hope. It's early to say for sure it's gonna work. But all of the things that you'd want to see by this stage are the things that we're seeing. So every reason to believe that we will have an effective vaccine sometime in the next six or so months, if things stay on track.In this particular one, they took pains to point out that there was a T-cell response. Can you talk about that for a moment?Yeah. Our immune system is complicated and has two different arms to it. One is the arm that relates to antibodies. Are you developing, is your body reacting and developing a set of chemicals that then can directly attack the virus? And then as a second part of the immune system that has cells called T-cells, and that is cells that also attack the virus. And the best immunity is that both arms of the immune system are working to kill the virus. You can get away with one or the other in some cases, but it's a belt and suspenders kind of thing: you want both. And the fact that a vaccine seems to stimulate both arms of the immune response is really hopeful news. And it means that even if one wanes over time, for example, there are some studies that seem to show that the antibodies may go up and may go down over time. It may be that you're protected better and longer by the second arm, the T-cell arm. That still has to be sorted out, but the best possible vaccines are the ones that stimulate both arms of the response. So that's really helpful.Okay, well, let's get to questions. We had a lot of them this morning sent in to askus@kcbsradio.com and I'll start with a short, simple one: do I need to wear a mask when I walk alone in my neighborhood?The rules in San Francisco are that you need to wear one when you're within 30 feet of someone. And the reason really is that when you're within 30 feet of someone, if you're walking toward them, you're going to be within six or eight feet soon enough. So in point of fact, if you are completely alone, the risk of you getting it or giving it is zero. And yet it probably is the right call for all of us to be wearing it when we're outside all the time, just as a matter of habit and to reassure everyone else that you're safe. When I'm walking around in my neighborhood, I have a mask on if there's absolutely nobody on the block with me, if I'm walking with the dog, I will sometimes sort of open it up my nose so I can breathe a little bit more easily, but it would be best if we wore them all the time.I got a couple more, this is obviously a hot topic these days. This next one says: I fully understand the idea of wearing a mask around others, but it gets weird. I ride my bike in areas where I'm easily 20 or 30 feet from anyone else at all times, do I really need a mask for that? And when I stop at a stoplight, the person in the car next to me has the window down, and isn't wearing a mask because they're not required to.Yeah, it's the same thing. I mean, if you are more than six to eight feet away from people, the chances that you are going to transmit it or get it from them are very, very low, particularly if you're outside. And so it really is kind of a pragmatic and messaging issue of, if you were completely alone, there's no risk of transmission. And yet sometimes you think you're alone and then someone walks around the block or comes next to you. So we're best off if we're wearing them as much as possible, but in terms of true risk of transmission, it really is when you're within six or eight feet.Six feet is not a magic number, by the way. There have been cases where people have been further away, because of the way the virus spreads has to do with ventilation sometimes. But, you know, certainly if you're more than 10 to 15 feet away, the mask doesn't add very much. The problem is, you know, you just never know. And if you're walking outside, someone just pops out of a house or comes out of a garage, or goes around the block so it's safer if we're wearing them most of the time,I encountered a track team running four abreast on a fire trail, none with masks, all talking loudly to each other and not giving way. How dangerous might this be for exposure while passing them?Low, but not zero. Outside is much, much safer than inside, brief contacts by people. If someone is walking by you at the store or running by you, the chances are very, very low but not zero. And so, certainly, if I'm outside walking and then people might be running by me, I want to have my mask on and ideally they would have theirs on too.Is there anything you should do after having a repairman in the house besides sanitizing surfaces? What about the air? This is assuming everyone wears masks and gloves. What about house cleaners? I want to have my whole house really cleaned along with windows, et cetera, not looking to necessarily sanitize, but just a good, deep cleaning. Being elderly I haven't been cleaning very deeply.Yeah. I mean, we've learned that the risk of surface transmission is lower than we thought in the beginning. So at the beginning, we were all obsessive about quarantining the mail and taking the shopping bags and wiping them down. Personally, I'm a little bit less so than I was, because it seems that you can get it by touching a surface, but it really would have to be that someone has just coughed or sneezed on it and you touch it fairly soon after that and then you touch your mouth or your nose: all relatively low probability events. Our house was getting to be a little bit of a pit and so we do have cleaners come in. When they come in, they wear masks. We're not in the same room with them, and soon after they leave, we just circulate through the house. It's probably a good idea to just not be in the same room as the person and insist that someone coming to your house is wearing a mask. But once they're gone, I think it's safe to go back to your normal life.Got a couple of questions around re-infection. One says: some evidence of people who were positive and then recovered to get re-infected, if this is the case, what's the benefit of a vaccine? And the other one, I just read a paper published end of May on the NCBI website about re-infection, the short version was there was still the need for more information. The conclusion was we must take into consideration the probability of genetic mutations as observed, rather than re-infection by the same strain.Yeah. There has still not been a single credible case. And I mean a case that has been reported in the medical literature and peer reviewed, I don't mean a case showing up on the internet. A case that we are confident it's real, in which someone had diagnosed COVID, tested viral positive, was sick - let's say went to the hospital - went home, got better, and then had another case where they tested positive again. Now, given that there have been millions and millions of cases, the chances that the antibody or immunity is not working, seem to me to be close to zero. If immunity did not work well, even if it was unusual, you'd still hear about hundreds of cases like that. And it's something everybody's on the watch for so much that we would be hearing now, you know, in New York City with all the cases they had in March and April, we're now three months later, you'd be hearing about many people coming back to the hospital with COVID. You'd certainly hear about it other parts of the country and the world.So it appears that this either never happens or happens incredibly rarely, which is really extremely reassuring when it comes to the matter of, will a vaccine work? It appears that once you've had the infection, your immune system gears up and prevents another infection, and there's no good reason to believe that a vaccine won't be able to do the same thing. The trillion dollar question of course is how long it lasts. And the answer to that is we have no idea. It may turn out to last months. It may turn out to last years and it may turn out to last for many years. If an effective vaccine comes out, that's still terrific if it lasts years cause that gives us a couple of years to figure out, do you get a booster and it works again? Or by that time, we'll have more effective therapies. Ideally, of course, the vaccine will work and last for many, many, many years. We don't know that yet, but I'm quite confident based on what we know that when you have the infection and therefore no reason to believe that when you have an effective vaccine, you won't be able to prevent COVID.I live with my wife, both 70 years old. If I test positive with no symptoms - asymptomatic - and she doesn't show any symptoms after 14 days are we COVID-free?So if you test positive, first of all, I would want her tested cause she's a contact, so I'd want to know for sure whether she's infected. As we've all seen, asymptomatic cases are common and represent about 40% of all cases. If you have tested positive and she remains both asymptomatic and is negative with a negative test after 14 days, as far as we know you are now out of the woods. You should be immune, as I just said, and she probably has gotten lucky. And now since you're exceedingly unlikely to get it again, she's now at the same risk she would be otherwise, but once she's out 14 days, she should be fine.
I understand zinc gives a tad of prevention, potentially, for the coronavirus. But there are so many forms of zinc in the market. I have three bottles: zinc as soy amino acid chelate, 10 milligrams; zincum aceticum 2x and zincum gluconicum 2x, combined in one chewy gummy drop; and zincum gluconicum 2x, 13.3 milligrams zinc in one lozenge. Which one should I take?Well, the chewy gummy drop sounds pretty good, but other than that I have absolutely no idea. And I would say that there is some theoretical reasons why zinc might be effective. There is no clinical trial evidence that says that it is. So it's probably not harmful, wouldn't criticize anybody for taking it, but there has been no good study that's been published that demonstrates that it's effective.As I recall, one prediction was that COVID-19 would drop off during the summer like other infections. Clearly this has not happened. What does this tell us about how this particular virus work, survives and infects as compared to the ones that tend to diminish during summer?Well it's interesting that it's really not clear why some viruses go down in the summer, whether it's something about the temperature or it's simply a matter that people are out and about more and not cooped up inside their houses. And we know that for many viruses, being outside is better than being inside, just in terms of being in more air and having more ventilation. But very clearly as we see the surges around the country, now this is not one where there's any seasonality at all. And all it tells us that it's acting like a regular virus. It's transmitted from one person to another and it has to do with proximity and has nothing to do with the temperature outside. That doesn't mean that sunlight doesn't help. So for example, if you have a virus on a surface and it's outside, we do think that UV light will kill the virus a little faster than it would if it was inside, but it doesn't seem to be a particularly important factor. By far, the more important factors are the distancing and the masks and all that.The fact that we've seen surges over the summer makes me even more worried about the fall. Because nothing about the temperature, I think, is gonna make a difference, but it's really all about human behavior. As people spend more time inside that will increase the risk of transmission because outside does seem to be safer than inside.Next one, when counties are reporting the number of cases, are they including asymptomatic positive test results or just cases of actual disease?No, they're reporting all positive test results. They should not be - and they right now are not - reporting people who think they have COVID. In the beginning, everybody who had a fever or muscle aches or a cough thought they had COVID and some of the early reports were of symptoms of COVID. It turns out that, you know, the vast majority of people who have symptoms of COVID don't have COVID. In the Bay Area, the test positivity rate is somewhere around 3-6%. So I can tell you, every person with symptoms thinks they have COVID, but that would mean that 19 out of 20 of those people don't. So the only cases that are being reported now are cases that test positive. And it doesn't matter whether it's with symptoms or without symptoms.At UCSF, because we're testing all of our patients with symptoms, as well as we're testing all patients who come in the hospital, or patients who need procedures like surgeries, or a cardiac catheterization or a colonoscopy, we actually are internally reporting both our positivity rate in patients with symptoms and without symptoms. So our overall positivity rate is about 2%; and that is about 6% positive in people with symptoms and about 1% positive in people without symptoms. I follow that ladder a number very carefully, because that to me is about the best approximation of, what are the chances that the person in an elevator with you in San Francisco, or next to you in the store on a line has COVID? And so our best guess is that's about 1% today. Whereas the overall prevalence in San Francisco, including both symptomatic and asymptomatic people is more like 2-4%.That's a very interesting number. Thanks for that. There's a pretty strong thread on social media, says the next question, claiming the case count is artificially high because every time a test comes back positive, it's another "case". In other words, one person who gets four tests with a positive result would be four cases. Is that true?I think that varies from region to region as to whether they are reporting it that way. I can't guarantee it, but I'm pretty sure San Francisco doesn't do that, they do it by individual rather than case counts. It's a legitimate concern. You'd have to look at how each region's reporting.How are we doing on contact tracing? Are counties doing an effective job? Can it be effective when so many asymptomatic cases are circulating?Well, we're doing well in the Bay Area because we have really world-class public health departments and California has invested a fair amount of resources in growing our contact tracing capacity. My colleagues at UCSF have helped build that and have helped train a whole lot of contact tracers around the state. The problem with contact tracing is that it requires that people are tested, the tests, come back quickly, the contact tracers then go out and find other people and tell them they've been in close contact, those people get tested and their tests come back quickly.So the big concern about contact tracing in the Bay Area is not so much the contact tracing, cause we're geared up to do it. It's that it all hinges on people being able to get a test and get the tests back quickly. And now that we're hearing about people who are taking a few days to get in for testing, and then the test doesn't come back for three to five days. If the lag period between you getting called about a contact and you getting your tests back is a week, it sort of defeats the whole purpose. Cause when they have symptoms or if they're asymptomatic, but are positive, that's the moment that they're at highest risk of both getting sick, but also transmitting to others. So it's very much dependent on getting our testing house in order. And that's been a problem. The tests were reasonably available a month ago and turnaround times weren't bad. And now things have gotten a little bit off the rails there.If a household of two adults and a 10 month old baby quarantines for two weeks after seeing a friend indoors without masks or social distancing, would it be safe for the 70 plus year old grandparents who have also quarantined to get together with the younger household members indoors and everyone without masks or social distancing?You know, there's no no-risk circumstances. There's essentially nothing you can do, where people who have been living separately then come together in a "unsafe" - I don't mean sort of in a cosmic sense, but in a way where we know the virus can be transmitted to people within six feet of each other, not wearing a mask - and say the chance of transmission is zero. I would say unless all of those people have been tested that day or in the last couple of days and you're sure that they're zero. With the story you just said, the chances that that household that had an exposure is infected from that exposure now is zero if it's now 14 days and everybody's fine. But in the 14 days, you said they've stayed in the house. I'm guessing that they went out of the house to go shopping or did other things. So you can't get down to a 0% chance that that will cause a problem. But I would say the chances are very low. If all of the parties have been extraordinarily careful and have had no contacts of consequence in the past past two weeks, that's about as safe as you can get. Still, if I was 70 years old and I was going to be getting together with my family, I would be insisting on everybody wearing a mask.Is vitamin D3 more helpful than other supplements in boosting the immune system, and thus possibly helpful in protecting against COVID?Possibly. You know, there's a literature out there on vitamin D being touted very widely on the internet. It's sort of like zinc. There's some theoretical reasons to say it might be helpful. There is no good clinical trial data that demonstrates in COVID that it prevents infection. So again, not harmful. If you feel like taking it, I certainly wouldn't be critical of it, but at least at this point, there is no vitamin or mineral that has been proven in a rigorous way to work. And the problem is, in the world of vitamins and supplements and all that, there are a bazillion claims and most of them don't stand up to scrutiny when you actually test them rigorously.