How Epidemiologists Understand the Novel Coronavirus - The New Yorker

“I don’t think we have a great sense of exactly why children are not getting sick,” the epidemiologist Justin Lessler said.Source Photograph by Miguel Medina / AFP / Getty

To discuss the latest developments in our knowledge of the coronavirus pandemic, I recently spoke by phone with Justin Lessler, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. Lessler, who has studied outbreaks of influenza, measles, and cholera, is particularly interested in modelling transmission dynamics as a method of controlling the spread of disease. Our conversation, which has been edited for length and clarity, covers the ways in which our understanding of the pandemic has improved, what we can learn from different governments’ responses, and why older adults seem to be more at risk of serious illness.

How has our understanding of the coronavirus changed during the past month or so, and in what ways?

I think in a number of ways. Some of it has just been confirming some things we suspected from SARS and other coronaviruses but were not sure of. For instance, we have a much better grasp of what the incubation period is now (an average of five days) and the generation time, which is the time between when a person is infected and when they infect somebody else (around six days). We are starting to learn a lot more about how infectious it is and the context in which it is infectious. We had signals of this a month ago, but now it is very clear that the age distribution of death and severe outcomes is stark, with older adults having quite high mortality rates, and young kids basically not dying at all. But we do now know that kids get infected. It was unclear why there weren’t cases before, but now we are relatively confident that they are getting infected. They just aren’t getting sick.

Can you apply some numbers to some of those things?

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We are pretty sure, based on the data from Wuhan, China, that about eighty per cent of deaths occur in those aged sixty or over, whereas less than one in a thousand occurred in children under twenty. So an extremely stark age distribution. One study I did with the Shenzhen C.D.C. found—and this is not yet peer-reviewed, it’s a preprint—that rates of infection were similar in young kids who were exposed and in the population over all. But, of course, we are not seeing kids getting hospitalized and dying, so we know they are not symptomatic of getting severe disease.

So anyone can get it, but it’s just how seriously it affects you?

Yeah, whether or not you get ill. What it means to get a disease is a little vague, but, if you are thinking about it as getting infected with the virus, it looks like anybody can do that. But, if you are thinking of what it means to get a disease as actually getting ill, then it appears that children are at least somewhat protected.

Do we have a sense of why that might be?

I don’t think we have a great sense of exactly why children are not getting sick. We have some good ideas of why older adults may be dying at higher rates than younger adults and children. But why children may not be getting sick at all or getting seriously enough ill to ever show up in the data is a little less clear.

Are there theories for why this is the case with older adults?

In terms of the older adults, I think there are three main theories. The first is that one of the receptors involved in this virus is also associated with cardiovascular disease, and that it might be exacerbating cardiovascular disease, which tends to be very present in older adults. A second is that older adults are just more frail, and that the populations that have been impacted have a high concentration of frailty. We will have a sense of how true that is as the disease enters populations where frailty is more evenly distributed across the population. But I think people think it’s a little more than that. A third theory is that it could be some sort of immunological priming. The idea is that somehow people above a certain age have been exposed to a version of coronavirus early in their lives that somehow immunologically primed them to have a more severe reaction to the current virus. I think evidence is still unclear around those theories, but they may be starting to form around one or the other.

What do you make of the idea of school closings?

I think that it depends on what you are trying to accomplish. If you are trying to stop the epidemic dead in its tracks, it is probably the thing to do. If you are trying to simply slow it, it’s a little more complicated than that, because we don’t really understand the role that kids are playing in transmission yet. We know they have been infected, but we don’t know if they infect others.

If people are infecting each other, and kids can get infected, why would they not be infecting others?

They rarely develop severe symptoms. And there are reasons to believe that, if you don’t develop symptoms and are less sick, you are less likely to infect others. It’s not that no asymptomatic kid will ever infect another person, but it might be the case that they are, say, a hundredth as likely to do so as a symptomatic adult, and we just don’t know.

What are the biggest lessons we have learned from China, South Korea, and Italy?

I would definitely say that what China has been able to accomplish has been quite impressive. They had a raging epidemic that looked like it was out of control, and by shutting everything down they managed to stop the epidemic in its tracks. That was an impressive accomplishment, although those are extreme measures we would really prefer not to take in most places in the world, and, if we had to do them everywhere, the repercussions of those could be quite bad themselves. And now Italy has had to do the same thing. South Korea seems to have done a somewhat better job of getting hold of things simply by ramping up testing and with more moderate social-distancing-type measures. Hopefully we will have a sense of how well that worked sometime soon.

What have you made of reports from labs around the world about the development of a vaccine? Would development be at all different in the midst of a crisis like this?

I think it is extremely important and something we should be working on. I agree that there is some worry that maybe things would be rushed out for trials in humans a little too fast. But I do think the scientific community has shown pretty good discipline with that in the recent past. We need a vaccine. A vaccine could make the difference between this being a disaster that there is very little we can do about versus something that can be contained and dampened down. Without a vaccine, all we can do is ride this out or stretch it out, most likely. And that is going to be a rough ride. A vaccine, or some highly effective treatment, is our main option for making it a smooth ride.

Most of the conversation around social distancing has been about large groups. Are you telling people in your own life to essentially quarantine themselves if that is what they are able to do, or is that too extreme?

Certainly anybody in my life over the age of sixty-five or seventy I have been telling that to. Certainly to anybody in those older age groups who is at very personal risk, I have been saying, “You should self-isolate.” I have been encouraging everyone else I know to minimize contact and lower the amount of contact that they are having, but, at this point, to try to think about what is sustainable for them personally.

How much trust do you have in the federal government’s response, and do you worry about the politicization of science?

I just try to focus on doing what I can and making the difference that I can, given whatever influence I have, by trying to answer what I see as the most important questions about the disease. I am going to dodge your question, in other words. [Laughs.]

What is your average day like now?

What my day is like? My colleague who has been visiting me is laughing because it is hectic. I get up, I get my kids to school, and then I am essentially working on coronavirus stuff or talking to reporters until I have to go. Pick them up at five-thirty, and get them in bed at nine. My wife is a resident working nights, so I have child-care responsibilities. And then I work until one or two, and then I get up at 4 A.M. for my daughter’s middle-of-the-night bottle and do it again. And hope I don’t collapse.

And what does the work mostly consist of?

It mostly consists of organizing other people, but a lot of it is focussed on running analyses and trying to get access to clean data, and helping to find partners who need help, but who also can provide information that helps the global response, and then working with them to understand their data, clean their data, and then run planning-scenario models and things like that that help them understand what is going on and what might be coming.

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