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Super-Spreaders: Expert Says 80% Of Coronavirus Spread Comes From 10% Of People

Published: Friday, October 23, 2020 - 1:00pm
Updated: Friday, October 23, 2020 - 1:29pm
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MARK BRODIE: The State Department of Health Services is reporting 975 new cases of COVID-19 today, along with six more deaths. Nearly 236,000 cases of the virus have now been confirmed in Arizona, including more than 4,700 reported since Monday. And 5,965 Arizonans have died from the disease.

STEVE GOLDSTEIN: Most of the country is seeing a strong surge of COVID-19 cases — Arizona obviously no exception, with the number of cases here nearly doubling in recent weeks. But we may have additional insight into who's causing that spike. So-called "super-spreaders," which can be people and events. During a news conference earlier this week, Arizona State University Biodesign Institute Executive Director Joshua LaBaer said that 80% of the spread can be attributed to around 10% of those who have the virus. And LaBaer is with me to talk more about the latest with COVID-19. Joshua, with these super-spreaders around us, how can and should people plan for this kind of thing other than wearing masks or maintaining social distancing? Does more need to be done?

JOSHUA LABAER: Right. So you're right on, on the right subject there. So there's been a number of studies recently which have looked at transmission rates. And one element of the studies there involves something called dispersion, which is how this thing gets transmitted. And what we have learned looking over a lot of data now is that it's not that everybody gives it to somebody and it's sort of a homogeneous dispersion, but the dispersion of the virus from around individuals is happening in these events, as you referred to them, oftentimes called "super-spreader events." And in those events, a few people give it to a lot of people. And probably the most dramatic of these was the Sturgis Motorcycle Rally in the middle of August in North Dakota, which took North Dakota the highest per capita rate in the country. And people believe that up to 250,000 people may have eventually gotten infected because of that rally. And the transmission is occurring from individuals possibly called or now called super-spreaders, people who spread it. And there may be two combinations that play a role here. Part of it may be the event itself, as you referred to, which is that having a lot of people close together, possibly not mask wearing that leads to rapid spread. And part of it may be the presence of these individuals. And it's not clear why they are super-spreaders. It could be that they have very high viral counts. It could be that somehow something about their biology stabilizes the virus in the saliva so that it's more transmissible from them. Other people have hypothesized that they have other viruses on board the same time, and the combination of viruses may in some way make them more likely to spread. We don't fully know, but that's what the math is telling us.

GOLDSTEIN: What sort of impact could that have on contact tracing or what sort of things would one need to apply to contact tracing ... considering there are people like this?

LABAER: One thing that that reminds us about is that there are two sides to contact tracing. One piece of contact tracing is if you identify an individual who's infected, you want to know who that person may have spread the virus to. So you want to talk to that person, say, "Who have you been in touch with?" But another piece of this contact tracing is what we call backwards contact tracing, which is to say, can we figure out where the positive individual got the virus? Can we go back in time and figure out where and when he or she got infected? Because it might have been at a super-spreader event, and that event may have involved a lot of other people who may have gotten the virus. And that would help us down the trail of figuring where else the virus may have gotten to. And so both sides of the contact tracing are important. And we are hoping that we can get both types of that information.

GOLDSTEIN: People would like to see a vaccine. There's a lot of work being done for that. When it comes to so-called super-spreaders, how does that affect the efficacy of a vaccine?

LABAER: I don't know that the super-spreaders necessarily impacts the vaccine efficacy, which involves a whole separate part of the system in terms of the immunity response. Or at least we don't know that there's a reason to suspect that super-spreaders would not also respond to a vaccine. What we need a vaccine for right now is to make it less likely for the virus to spread in our community. I mean, in effect, one metaphor for the virus is a fire that's burning through a city. Right now, everything to this virus looks like untouched wood. And so it looks like it could burn. If you could spread water all over everything so the wood was so wet and wasn't really flammable anymore, that would limit the spread in the community. And that's what effectively a vaccine would do — take a lot of stuff that currently is flammable out of the picture and make it less likely for the virus to move around.

GOLDSTEIN: So we are at a point that we are seeing more of a surge certainly all across the country. Arizona's scene looks like about double the cases we were seeing when things were heading downward. Did you anticipate this would probably happen? And if so, have we learned some lessons at least as a community that we didn't know four or five months ago?

LABAER: Well, you know, I don't want to say that we anticipated another surge. But on the other hand, I think we all know that this virus is here for a while. We're not going to get rid of it immediately, that's for sure. It's here. It's spread widely through our communities. And it is always a game of constant suppression. We can't rid ourselves of it, but we can suppress it by mitigation factors. So we kind of expected that it might come back again. What I'm hopeful of is that our lessons from the summer proved to us, without a doubt in my mind, that the mitigation factors work. At one point Arizona had the highest per capita rate in the world. We were leading the planet in terms of how much it was spreading. And we managed to bring it down to very good numbers by instituting common-sense measurements, by wearing masks, by staying separated, by not going out too much and then getting tested a lot. Those things all played a role in bringing our numbers down. And the hope would be that people realize it worked before and they would be willing to maintain those factors now. And we all understand, COVID fatigue. We're all tired of wearing masks. And our whole species is hardwired in our DNA not only to look at faces, but also to make faces that convey emotion, that convey information. And that's how we communicate as a species, at least in part. And having to wear masks limits that, of course. But we also know that this virus has figured out how to surf on saliva droplets from one person to another and transmit the virus. And we've got to limit that.

GOLDSTEIN: That is Joshua LaBaer He is executive director of the Biodesign Institute at ASU. Joshua, thanks for the time. And stay well. We appreciate your work.

LABAER: All right. Thank you. Take care.

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