Answering Your Questions About Virus Transmission

Stan Bunger
May 27, 2020 - 1:37 pm

    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 expect to see some milestones in the pandemic: 100,000 deaths in the United States and 100,000 cases in California. With that in mind, we're talking about where things stand with the coronavirus pandemic and what all these numbers and statistics mean with Dr. David Dowdy, professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

    These are fascinating times - obviously terrifying for some - but for people in your business with the tools that you've come up with in real time, tell us how many of these data platforms and dashboards and so on that we're now seeing and using were around before this and how many have been created on the fly.

    So there are quite a few of these dashboards around. I would say most of them have been created since the onset of the pandemic, but using tools and knowledge that we had from before. So it's not really on the fly, but I'm not sure that they were around two years ago.

    And let me ask you also about the speed at which data travels. This thing is happening in real time, we live in a 24/7 cycle of information now and sometimes it feels as though it's hard to get that information shoved into the pipeline fast enough.

    I think we have pretty good systems for data capture now and we live in a big data world and a lot of our research is based on big data science. We're able to capture case counts on an hourly basis, if not better. And this data plugs straight into many of these models, dashboards, etc. So there's always room to grow but I think that as far as getting data out and accessible, we're doing pretty well.

    So just out of curiosity, how does that work on the back end? At the point where a case is diagnosed or a death is confirmed, how does that information get into this great big tub of data?

    Each reporting authority - so let's say a state, for example - has a site where they plug the data in. Then there are different systems to grab the data automatically as they get plugged in and upload them straight away to another site. For example if you were to get a lab test from your doctor, once the lab gets the result they enter it and it's available to everyone who's looking for it.

    And are all of the nations on earth and all of the states in the union and all of the counties in each state doing the same thing or are there ups and downs in that?

    Certainly ups and downs. I think that getting the data into that initial port can take a long time. It can take anywhere from a few hours to a couple of weeks, but once they're in that initial port the data moves pretty quickly.

    Let's get to questions here, and those can be sent in to

    I understand that restrictions were put in place to “flatten the curve” and keep infection rates low. What I do not understand is what happens as restrictions are lifted? Won’t we be right back when we were in early March: a population with little immunity and infections likely to occur? 

    That's a great question. I think as restrictions are lifted we will be a population with little immunity and I do think infections are likely to occur. I think it is important to remember that life now is not the same as life was in January or February. Even if we're lifting restrictions, people are going to be acting in different ways and we're not going to be saying, "go back entirely to life as it was before." How much of a difference that makes? We don't know yet and we can only find out over time. But it is true that we're going to be a population with little immunity and high risk of infections occurring.

    Can you really measure the impact of changes in the rules; i.e. if some place allows restaurants to open at X-percent of capacity and another keeps them closed, do the numbers show anything?

    I think we would love to be able to do that and people are trying to construct models to inform some of these sorts of policy decisions, but it is really difficult to get data at that granular a level. Especially since there are delays in reporting, you don't know if someone who comes in was infected at a given restaurant or anything like that. So it's a real challenge, I think we're trying to do the best we can.

    What about these contact tracing apps I'm hearing about? Some places are already launching these - parenthetically, I think the French Parliament is voting today on one that is supposed to kick in here on Monday. This questioner says, how will the information from these help you understand the pandemic?

    That's going to depend on what app you're talking about. If it's an app for people to give data on where they have been and that's someone who ultimately tests positive for the disease, then that gives us some information about where transmission might have occurred. If you're talking about apps to help the contact investigators themselves, then it can help us to collect the same sorts of data from multiple different people and then we can collate the data and analyze it, which is certainly better than having just piecemeal different collections from different people.

    How does the trajectory of the pandemic in the US compare to what we've seen in other countries? Places like Italy and Spain seemed to have so much trouble early on but now maybe not so much.

    The trajectories have been very different in different countries. Italy and Spain both had very strict lockdowns and saw pretty substantial declines in their case numbers. Places like the U.S. and Sweden have seen flat numbers of cases declining slowly, but certainly not to the level that you saw in Italy and Spain and also say, South Korea. Then there are other countries like Brazil where the numbers are still going up. So we're on the high end but maybe on a per population level, not the worst.

    So what conclusions can you draw at this point, or is it too early to draw any about quote-unquote "what works" or didn't work?

    Yeah I think that what we know is that the social distancing measures that were put into place did work. Before that happened, we were seeing doubling in the size of the epidemic every three to four days. After that, we've seen flattening of the curve. But what's important now is to understand which components of that response were the most important and which things maybe we can ease up on without increasing substantial transmission of the virus. And that's stuff that we still don't know right now. 

    I read everyday and I hear everyday about testing, testing, testing. Why is this so important?

    There are a number of reasons, but one reason that testing is so important is it allows us to prevent outbreaks before they start. So we are able to identify certain types of populations that may be at risk for outbreaks, whether these are people who are living in congregate settings like prisons or long term care facilities or people who are working in settings where they see lots of people, whether it's grocery workers, etc. If we're able to test those people and know when they test positive early in the course of things, then we can prevent that outbreak from happening in the first place as opposed to mopping up afterwards. And if we're able to prevent outbreaks even on a small scale, you add those up over the whole country and that's going to make a big difference in the epidemic.

    And this question didn't come in from a listener but somebody asked me the other day, so I'll pose it now. Because so many of these outbreaks seem isolated to places like you just described - prisons, long term care facilities, meatpacking plants, places with people in close contact - wouldn't it make more sense to focus on those and relax things for everybody else?

    I think the thing to consider there is that you really have both. So if I were to estimate - and I don't know for sure - I would say that probably somewhere between 25-40% of transmission occurs in those sorts of outbreak settings, and the remaining 60-75% occurs along people who only infect one or two other people. It's certainly very important to focus on those outbreak settings, but that's not still where the majority of transmissions occur. So if we focus only on the outbreaks then we're going to be missing a lot of transmission. But if we do a good job of preventing those outbreaks, we can make an important difference. 

    Is it still unknown if having had COVID-19 gives a person immunity? 

    If someone has had COVID-19 and has recovered, then they have had millions of viruses in their body and they have gotten better. So by definition, in a way, they have immunity. It's unlikely that if you added a few extra viruses to the mix that that would have changed things very much. What we don't know is how long that immunity lasts. I think that if someone has had COVID-19, they just recovered and you re-infect them a week or two later, they're probably not going to develop the disease again. But I don't know how long you have to go before they lose that response.

    How does the amount of virus droplets you're exposed to factor into the eventual severity of your illness? Does this depend on one's own immune response?

    It certainly depends on the immune response, because we know that there are some people who die of COVID-19 and other people who get infected and recover and never even know they had the disease. The main difference between those people is probably related to their immune response. It's possible, likely even, that to some extent the amount of virus you're exposed to changes the course of the disease but that's a lot less certain. You have to remember that once the virus gets in your body, it starts to multiply at an exponential rate so very, very quickly. And so the difference between getting exposed to say 100 viruses versus 1,000 may not make that much of a difference. But it's an important consideration and something we need to be thinking about as we think about the future of the epidemic because if it's true and we can limit the amount of exposure people have, then maybe we can see fewer deaths even if we have the same number of cases.

    This one comes up a lot too in different forms: how do I know how much I'm being exposed to in various environments? I think some people feel that one virus, one particle can do the deed and others are of the opinion that you might have to be surrounded by millions of them before you can get sick.

    Yeah. So I think that one virus probably is not going to cause disease in most people. At the end of the day, it's a matter of how many viruses get through your initial immune response. And so viruses can get trapped in droplets, in your lungs and never make it into your body, etc, etc. I remember doing a zombie run, right? And there are a lot of people running and there are zombies trying to tag you, what have you. If you have a lot of people getting through, then someone's going to make it through. Whereas if there's only one, then probably not. So the more viruses you're exposed to, certainly the higher the risk of infection. 

    So time and distance, it's kind of like basic high school math right?

    Yeah, in a way.

    How dangerous is domestic air travel right now?

    Certainly the airlines are doing a lot to try and reduce the risk of spread in that environment. And so I think it's certainly less risky to fly than it used to be. In general, I think it's not the safest thing one can do but probably not the riskiest either.

    Why don't we see more data on "survival rates" for the coronavirus? Wouldn't that be a useful number for each of us to assess risk?

    We certainly see mortality rates, and so survival is just the opposite of that. If we know that for example, 1-2% of people who get this disease die, then that means survival is 98-99%. But that still means a lot of people die.

    Let me ask you, because early in this the denominator problem was something everybody was talking about. We didn't know how many people had been infected so we couldn't say what the mortality rate was. Do you feel like we're moving into a better understanding of that?

    Moving, yes. But we're not really there yet. I mean we still don't have a great sense of how many people have been exposed. We know how many people come into the hospital and I think we're doing a better job of testing people as they come in with symptoms, but we still don't know how many people are out there who are being exposed and never get sick. We have ideas, but we're not there yet.

    What would it take, in terms of percentage of the population being tested, to have a number that you would be comfortable with? We're reading that in Wuhan, everybody's being tested. Obviously that's not gonna happen here anytime soon.

    So it's actually to me not so much about the number of people as the representativeness of people. If you were to have a fully representative population, a few hundred could be enough to give you precision on that estimate of number infected. But the disease is so heterogenous that it's really difficult to find that representative population. What's representative of New York City is not what's representative of San Francisco and that's not what's representative of Fargo, North Dakota.

    How is a public health isolation order enforced to confirm that infected people actually stay home and comply with the order?

    How is it enforced? Well that's going to vary from state to state and city to city, so I'm not sure I have an answer for that that's going to work for everywhere. 

    Fair enough. Are we losing our immunity by sheltering in place? What can herd immunity do for us?

    So we're not losing our immunity by sheltering in place. But by hopefully exposing less of the population, we are having hopefully fewer people exposed. Ultimately, if and when we get to a state of herd immunity, whether through infection or hopefully a vaccine, we will be able to keep transmission levels of the virus at a low level of the population. But we're really a long way away from that. Right now, maybe 5% of certain populations have been exposed. That means 95% have not. So we're not losing our immunity by sheltering in place, we're hopefully buying time until we can get a vaccine that can get those immunity levels up.

    What's your optimism level on vaccines, based on everything you know?

    I'm cautiously optimistic. I don't think that we're going to have a vaccine in the next four months, but we have a lot of candidates out there, a lot of activity and a lot of early promising results. So I think ultimately, hopefully, we'll get there. But it's probably going to be 2021 before we have that vaccine.