MARY LOUISE KELLY, HOST:
In the middle of March, Jonathan Smith posted a letter to his neighborhood Facebook group. Smith is an infectious disease epidemiologist at Emory University. With coronavirus cases beginning to pile up in parts of the country, he felt compelled to warn his neighbors of what he called the unforgiving math of epidemics. Social distancing might start off feeling futile, he told them. Confirmed cases and deaths will rise, and you will feel discouraged. But, he urged, hold the line. Well, that post went viral, and Jonathan Smith joins us now.
Welcome.
JONATHAN SMITH: Thank you so much for having me.
KELLY: Glad to have you with us. So I mentioned you wrote this letter mid-March, three weeks ago. It feels like we have been social distancing forever at this point. It also feels like it's going to last forever. Your message is, I know it feels that way, but don't give in. Don't cheat. Why is that so important?
SMITH: So it might be better if I take a little bit of a broader step back and look at how these social distancing measures kind of interplay with other interventions that we have. So we, as epidemiologists - when we consider if an epidemic will grow or if it will shrink and the rate at which it grows or shrinks, we think of three broad categories.
KELLY: OK.
SMITH: So the first thing that we think about is the duration of infectiousness. So how long is somebody infectious? The second thing we think about is kind of biologic in nature. If someone is exposed, how likely are they to become infected? And the third thing that we think about is, how often do susceptible individuals come in contact with infectious individuals? And so using those three kind of bends of information...
KELLY: Yeah.
SMITH: ...We design interventions based on that.
KELLY: OK.
SMITH: And so for any - that's for any pathogen. And in the context of COVID-19, we don't have any clinical evidence that there is a treatment or a cure, so we're not able to shorten the duration of the infectious period. Biologically, this is quite an elite pathogen that we're dealing with. And so it is extremely infectious, and so the probability of infection if you're exposed is quite high. So what we're left with are ways in which we can figure out how to intervene from infectious people coming in contact with susceptible people, and there are a lot of ways to do that. So social distancing isn't the only way to do that. But if you...
KELLY: But your post - and I think, you know - if I can just lower us right down to layman's terms, I think it caught so many people's attention. This was my read, and I'd love for you to kind of, you know, tell me if I got this right. But just the tiniest bit of additional connection leaves very little benefit to all of the other efforts. I mean, I was thinking of an example, and it sounds like what you're saying was if there's even a minor breach, if I decide to sneak out and have coffee with one friend, it undoes everything else, all the other sacrifices that we've - that I've been making for three weeks.
SMITH: Right. So it's a difficult thing to think about transmission dynamics on a population level. So we naturally think, what if I get infected, or what if I infect people? But as epidemiologists, we think about the network dynamics that occur there. So if you sneak out for coffee, you are not the only person doing that. And so on a population level, the risk of infection and the risk that transmission will continue to occur - those risks rack up quite quickly on a population level.
KELLY: Yeah.
SMITH: And so, you know, I think one way that I just - this might not be the best analogy, but one way that I describe it often is it's kind of like a diet, right? So no diet says you can't eat. You have to eat. And so we have to breach these social distancing measures. But if you make smart choices in your diet and if you adhere to it quite well, then you'll be much more successful than if you begin to kind of cheat a little bit and sneak a donut here and there. So the same thing applies to these social distancing measures on a population...
KELLY: Yeah.
SMITH: ...Kind of scale. If we - there's always a little bit of weakness, if you will, in these social distancing measures. It would be quite naive of us to think that there would be 100% compliance. But it's - really, what we're talking about is - are these additional risks, these - the ways that people put themselves at risk of exposure that isn't necessary. I mean, if we can cut those out, we can, you know, really be much more effective in this intervention.
KELLY: And just briefly, in a letter to neighbors, you were at pains to write, hey; this is not my opinion. This is based on science. This is based on the math of how infections spread. Just briefly, though, people cheat. I mean, what happens if some people are really good about social distancing, and then just a small handful aren't?
SMITH: So, you know, this is an analogy here. It's something that can has kind of been borne out in a lot of the STD or HIV literature. So it's a common thing among HIV researchers that say your risk is only as good as your partner's risk because your partner is connected to someone else who is connected to someone else, and transmission occurs along that entire chain. So on an individual level, if your family or your household or your unit, whatever you're social distancing with...
KELLY: Yeah.
SMITH: ...Is adherent, they're only as safe as the leakiness of the most leaky person. And so, you know, at this stage in the epidemic, naturally, people become frustrated. And there's a lot of these challenges that are associated with these measures because it's not easy, right? It's not an easy thing to do. There's a huge mental and emotional toll to do this. But by its nature, you know, from a transmission dynamic standpoint, the disease doesn't necessarily care about why or who's doing it.
KELLY: Right.
SMITH: It just matters that it's happening. So if there's social interaction, this disease specifically, in its kind of unique ability to be highly infectious, is going to capitalize on any one of those kind of cheats.
KELLY: Just quickly - you've just finished your Ph.D. I know you're waiting for the diploma to be sent. Congratulations in advance. Did you ever expect, when you chose your field, to be in a situation like the one we all find ourselves in today?
SMITH: I never expected to be interviewed by Mary Louise Kelly about transmission dynamics.
KELLY: I'm talking about global pandemic, not being on NPR.
SMITH: That is not something that I ever expected.
KELLY: Jonathan Smith, an infectious disease epidemiologist. And he begins a faculty position at Yale in the fall.
Thanks so much for coming and talking to us.
SMITH: Thank you.
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