Coronavirus (COVID-19): Press Conference with Marc Lipsitch, 03/11/20


You’re listening to a press conference from the Harvard T.H. Chan School of Public Health featuring Marc Lipsitch, professor of epidemiology and director of the School’s Center for Communicable Disease Dynamics. This call was recorded at 11:30 am Eastern Time on Wednesday, March 11. 

A previous press conference is linked at the bottom of this transcript.

MARC LIPSITCH: Thank you. Thanks, everyone, for joining. I think I’d like to say a few things about where I think the situation is now on COVID-19, and then spend most of the time on questions.

My perception of the last several days is that the big question in the United States is whether we are in the phase of moving from containment and contact tracing to mitigation. And my strong view is that we should be very much moving to mitigation. And I can talk about what that means in a minute. But I think many health departments are finding it overwhelming to trace contacts and to quarantine those contacts and isolate cases. They’re finding it takes away from their other activities that are also important.

And I think as an epidemiologist, I can say that, in a setting of very, very limited testing, where most cases are probably going unrecognized, the value of case-based interventions is limited because if you’re only catching 10% of cases — and that’s an arbitrary number — then, at most, the interventions on those 10% can reduce transmission by 10%. But we have an infection with a basic reproductive number around 2. So that means that we need to reduce it by 50% before we can bring the curve to be level.

So there’s even a Twitter hashtag now saying flatten the curve. And I think that is the goal of mitigation measures. And those mitigation measures are multiple. They involve reducing social contact in every possible way. The reason — I mean, the recent Biogen conference in Boston I think is a nice example of how a business meeting can turn into a large transmission event.

I would love to know more about what the conditions were there. But many businesses are asking, should we cancel meetings, should we have people work from home. And I think the answer is yes, to the extent possible, this work needs to be done virtually as much as possible to reduce social contact. Obviously not everyone can do that.

Another category of social distancing, besides reducing aggregation of people, is to make it possible for people to stay home when sick. I’ve heard a lot of accounts of no paid sick leave policies, even in hospitals, which is completely insane. But it’s something we need to do not just in hospitals, but as a society we need to find ways to incentivize people to keep themselves apart from others when they’re sick.

And so the incentive issues around social distancing. It seems like different jurisdictions around the country are finding different levels of concern about public gatherings. The Indy 500 is still planned, with 200,000 or 300,000 spectators. That’s a lot of people. So there are a number of aspects of social distancing. We can talk more about those.

Why social distance now, when in fact most parts of the United States are not in crisis? We posted a preprint yesterday, and are submitting it for publication today, which describes the situation in two cities in China, Wuhan, where the epidemic started, and Guangzhou, where the epidemic was transported from Wuhan and started a bit later.

And what’s very striking is that the need for intensive care beds in Wuhan on the highest day in an epidemic that was not controlled for quite some time after it started, the need for intensive care beds on a per capita basis was equal to the entire capacity of the United States intensive care beds in Wuhan.

Obviously, Wuhan is smaller than the United States, so I’m talking per capita, not absolute numbers. But we have about 2.8 beds per 10,000 — intensive care beds per 10,000 adults in the US. And that was the bed occupancy, or that was the number of critical cases in Wuhan on the highest day.

The other thing to say is that the highest day for intensive care demand in Wuhan was about 3 and 1/2 or 4 weeks after the control interventions were put in place, because some transmission continued after they were put in place, and people take a long time to need intensive care from the time they get infected. So the situation we should be worrying about is the situation four weeks from now, not the situation now.

That’s hard for people to get their head around, but it’s really important. And I think a little bit closer to Boston, we have the example of northern Italy, where the same thing is happening, and intensive care is being overwhelmed. Doctors, pathologists, neurologists and other kinds of people are being asked to be internists because they need every doctor to take care of the COVID patients. It’s really chaotic. And this is what we’re trying to stop by flattening out the curve.

Guangzhou is a nice example of flattening out the curve. Guangzhou intervened with social distancing measures on the same day, but at a time when they had zero deaths confirmed and seven cases confirmed in Guangzhou. And they had about 1/100th of the peak level that Wuhan had.

I think the urgency is all the more acute because we will not likely be able to do the same kind of social distancing as China as effectively, for all sorts of reasons. But my view is that we really need to act immediately. Every place in the United States, in my opinion, is in one of two situations. Either we know there are a lot of cases, or we haven’t looked. And for that reason, I think it’s not too early to assume that there are a lot of cases in the places that we haven’t looked, and to start these activities now.

There is obviously much more to say, but I think I’ll be guided by your questions about what you’d like to discuss. So I’ll stop here.


OPERATOR: At this time, we will open up the floor for questions.

Q: Hi, Dr. Lipsitch. Can you spell out exactly what steps you think should be taken in the United States right now, really, really clearly and specifically? Schools, conferences, businesses, what needs to be done that isn’t currently being done in terms of mitigation and when you talk about social distancing? Are we talking about closing theaters, closing movie houses, not having parties? What are we talking about here? What about schools? What about businesses?

MARC LIPSITCH: I want to put schools on a side burner for a minute because I think that’s the absolute hardest one. As I told a European reporter this morning, what’s left of the American welfare state is so much channeled through schools that closing schools in the United States is a bigger decision than almost anywhere else. Apart from the educational losses, we have loss of nutrition for children, loss of mental health services. And then everybody has — no matter the U.S. or otherwise, there’s the problem that you lose essential workers from the workforce because they’re taking care of their kids.

So I don’t actually have a good answer on schools. I think we’ll come back to that at the end. But I think that’s the hardest one. In terms of the other activities, my view is that closing down meetings of large groups of people — and there’s no magic number. Harvard has said no more than 25 people in a room at the same time.

I think that’s a good number. It depends a little bit on the size of the room and the ventilation and the humidity. The New York Times carried a nice op-ed pointing out a few days ago those things matter to whether there’s a lot of transmission in buildings. So there’s no magic number, but I would say 25 is a good conservative one.

I think that implies that, yes, movie houses should be closed. It implies that theaters should be closed. We need to learn more about what happened at the Biogen meeting in the Marriott Hotel in Boston, but for business meetings like that that I’ve been to, you know, it’s not a lot of very close contact. There’s a lot of handshaking and there’s a lot of ordinary interaction between people. And that clearly spread infections to dozens of people.

So I think that indicates that there’s a real danger of accelerating the epidemic if you have large numbers of people together. So I would recommend, to the extent possible — and everything has a cost, and I think it is important to say that if there’s a meeting that for some reason is important for life or limb, that’s much more important to have than a meeting that’s important to venture capital.

So there’s a hierarchy, and we can think about costs and benefits in individual cases. But the goal is to minimize the number of contacts between people. So houses of worship is another one. I think we are at a point where we really could have our hospital system in crisis in three or four weeks, and that what we do now will affect that. And it’s better to overreact than to under-react.

As I said, I think the other category of ways of keeping people from contacting each other, we’re not going to be able to test mild cases of illness. And increasingly, as the weather gets warmer and it’s no longer flu season and no longer cold season, if you have a respiratory infection, it will probably be COVID-19.

And that will become more and more true as the other ones diminish, as they do every year. So leave policies for workplaces for sick people are absolutely essential. And I’m surprised to see how little action there has been on that front so far, especially in the health care sector.

To come back to schools, one of the — I told you some of the reasons why it’s costly to close schools, especially in the United States. One of the other aspects, of course, is what is the benefit. And that’s what jurisdictions around the country are wrestling with right now. In my view, the benefit is if you were just going for disease control, you would close the schools because children do get infected.

Some evidence, probably the best evidence, although it’s a small study, from Shenzhen, China, in collaboration with Johns Hopkins, suggests that children get infected at the same rate as adults, it’s just they’re much milder symptoms so you can’t tell it, and you have to look harder to find them. So if they’re infected and if they’re producing enough virus to test positive, then they’re very likely also transmitting infection. But the direct evidence of that is limited.

And compared to an infection like flu, where children are clearly important centers of transmission to the rest of the population, we don’t know that yet for this virus. So that’s why the benefit of closing schools is more uncertain. And so it’s really an agonizing choice between two bad options that people are trying to make. I essentially sympathize with the choice, and don’t have a criticism of their decision at this point.

So those are some of the key items. A lot of people are asking about travel. And on that area, I think it’s a subtle point. Travel on an airplane is maybe not terribly dangerous. It’s pretty tightly packed, but the air is actually filtered pretty well there. So if you practice good hygiene and handwashing and the like, it might be OK on airlines. I don’t think we really have any data yet. There haven’t been good examples that I know of of airplane-based outbreaks of COVID-19, but it might be hard to tell.

So I’m not sure what to think about airplanes. Public transport is another kind of travel, and I think that is much more densely packed in some places. And again, there’s a huge cost to closing it, and a significant risk of transmission, I would expect, in keeping it open because of the density of people and usually poor ventilation, especially in subways. But again, I don’t think we know that yet from data. I think that’s an inference from what we do know.

So I think travel is inadvisable because you’re in crowded airports, you’re in potentially crowded other means of transportation, and because you’re often going to either to visit an elderly relative or to go to a business meeting. So I think those are all reasons not to travel. But it’s not clear to me that the act of getting on an airplane, for example, is one of the most dangerous things. I think it’s just not known yet out there.

OPERATOR: We’ll take our next question.

Q: Hi, Dr. Lipsitch. Can you hear me okay?


Q: OK, great. Thanks for having this call. I wanted to ask you actually about some of the data indicating, you know, apparently much higher risk for older people and people with underlying conditions. So I just wondered what you think of some of these numbers that have come out of the studies — the data from China as they apply to other countries, like the U.S., and do you think these groups are at higher risk of mortality from this disease than from any other infectious disease compared with the overall population, or is this more kind of the usual high risk that these groups face from infectious diseases generally?

MARC LIPSITCH: I think it’s too early to say that. I mean, the largest numbers of cases have come from places where we really don’t know all the denominators. And it’s really hard to compare it against other infectious diseases. Certainly seasonal flu does take a bigger toll on the elderly, although interestingly, not — most of those seasonal flu deaths in the elderly are not from pneumonia or from the direct influenza, they’re inferred from the timing of deaths from respiratory and circulatory — sorry, from circulatory — well, yeah, respiratory and circulatory, excluding pneumonia. So I don’t know how to make that comparison. It’s very hard to do it apples to apples, especially with poor data.

I think that we just have to see in the United States what the risk groups are, and whether they’re the same. People have pointed out that, in both China and Italy, there are high rates of smoking. And of course adults, older adults have smoked for longer and done more damage to their lungs, typically.

So there may be an aspect of smoking as a cause of an age-related increase. That’s purely hypothesis at this point. As far as I know, there’s no data. There’s one weird paper that actually suggests the prevalence of smokers is low among the dead cases in China. But it was about 100 or so. It wasn’t a large study, and it’s hard to believe.

But so I think we have to be a little humble about extrapolating any one experience to other places. But on the other hand, it is common for infectious diseases, as you say, to be more severe in the elderly. And so I think this is probably not a China-specific observation. And we’ll just have to see how it differs or is similar to here. I would expect it to be roughly similar, but maybe some differences in the magnitude of the increased risk.

OPERATOR: We’ll take our next question.

Q: Hi, thanks. I’m wondering, as we’re moving from containment to mitigation, what is the role of testing? Because now there’s a big effort to ramp up testing of private laboratories. Is that worth the trouble? Do we need to be testing?

MARC LIPSITCH: Absolutely. We are nowhere near what we need, and we won’t be anywhere near what we need for weeks, at least. My understanding last I heard, which was a few days ago, was that no major hospital — none of the major hospitals in Boston had much testing capacity, if any. And they were all relying on the Department of Public Health.

To give you a sense, the estimate from CDC was that a few thousand — I think it was 5,000 or 6,000 — tests had been run by state health labs across the country up to that date. I think that was yesterday or the day before. I’m not sure of the exact number. To give you a sense of comparison, the province of Guangdong in China tested over 320,000 people in a 2 1/2 or so week period just for surveillance.

So that province of roughly a third of the population of the United States did about 100 times more tests in two weeks than we’ve done in the whole epidemic. It’s absolutely inadequate, and every effort needs to be made to ramp up testing capacity as fast as possible, for two reasons.

First reason is for clinical care and protection of health care workers, so that you can diagnose cases and you can figure out who needs to be treated with personal protective equipment. And the second is — and also figure out when people stop shedding virus. That’s also important. And then the second is for public health purposes, which is to understand the course of the epidemic, to figure out if there are more cases this week than last week or fewer.

And for that, you have to have surveillance systems in place that are running the same kinds of tests on a similar population every week. Doesn’t have to be on everyone. We don’t have to go and find every person and test them. But we need a representative sample. And there are ways of doing this that will give us a handle on whether the epidemic is going up fast, going up slowly, coming down, or what.

And if we don’t know that, then we won’t know whether any of our social distancing interventions are working. We won’t know whether we need to add school closure on top of other interventions because they’re not good enough, or whether we’re actually controlling things. It’s utterly inadequate, and it’s not moving anywhere near fast enough. This is the biggest debacle so far out of quite a number of debacles in the handling of this epidemic.

Q: Can I ask another question? Do you —


Q: — talking about the Biogen conference, were you surprised? I mean, we’re talking about 70 cases in Massachusetts alone. There were only 175 people at the meeting, although some of the cases were contact with people at the meeting. And then there were a few others in other parts of the world. Were you surprised that that many people got infected in such a short period of time, and what does it tell us about how this virus spreads?

MARC LIPSITCH: I haven’t gotten much information about the details of that meeting. It is a surprisingly large number. I don’t know what they did at that meeting. I don’t know if they were demonstrating some product that might have had some —I have no idea what happened. But it’s possible that there was a super-spreading event, that there was one person who was just very infectious.

We know that happened in SARS. It hasn’t been documented conclusively very much, if at all, to my knowledge, in this outbreak, but there’s certainly a suggestion that there are people who are more infectious than others. But in SARS, most people infected 0 or 1, and some people infected 25 or 22. So maybe it’s an example of that, and we just hadn’t seen that before or hadn’t recognized it. Maybe there were multiple infected people there already, and we didn’t see that.

But it does show that, with some frequency — we don’t know how typical, but a big meeting, or a medium-sized meeting, can lead to the transmission of a lot of virus to a lot of people, or of virus to a lot of people. And I doubt that every meeting of 175 people will lead to 70 new cases. If it does, the whole thing will be over very quickly because we’ll have a lot of infections very quickly. But it does show the potential of meetings to transmit virus.

Q: Do you think the Boston Marathon should be canceled?


Q: Even though it’s outdoors, there’s still a danger?

MARC LIPSITCH: We need to figure out what the relative risks of outdoors and indoors are. You know, there’s been a lot of discussion, and I said to the — well, there’s a lot of discussion about St. Patrick’s Day Parade, which was canceled in Boston, Philadelphia, and so on — many other places. Canceled in all of Ireland. And that question has come up. It is thought, in 1918, by many people that the parades to sell bonds for World War I in Philadelphia and maybe elsewhere were part of what set off the epidemic in those cities.

And I spoke to Boston city officials when they were thinking about this, and I said, I’m not totally convinced that that’s true because they were outdoors, and it’s not totally clear that a parade or a marathon, which is similar because it’s people standing close together on the sidelines, is a venue for a lot of transmission. But on the other hand, it’s not just the outdoor part. People have to get to it, which means probably riding public transport, in many cases, in very crowded conditions.

People are very closely packed together on the sides of the marathon as spectators, and are presumably having human contact with really relatively large numbers of people. So yes, it’s outdoors, and maybe it’s not as dangerous as some other things, but I think at the moment, we don’t know. And I was informed, because I’m not a big St. Patrick’s Day person myself, that, for example, the St. Patrick’s Parade is a parade, but it’s also a series of house parties.

And so that’s also a lot of gatherings of people in relatively tight quarters, potentially. So I don’t think we can prove which gatherings are most dangerous and which ones are less dangerous, except with the general principle that ventilation and humidification help reduce transmission and dry, unventilated places are bad, and that density of people is bad.

So we have some rules of thumb, but it’s really hard to say this event will be a major venue for transmission. But I think we need to err on the side of caution at this point. And that’s about the most dovish view I think you’ll hear. I mean, it really is widely believed that the parade in Philadelphia was the start of major transmission of their flu epidemic in 1918.

OPERATOR: We’ll take our next question.

Q: Thank you, Dr. Lipsitch, for taking the time to do this. I have another sports-related question. I take it from your earlier comments that you would not think it prudent to have the NCAA tournament, this massive event held with fans. But I’m curious what risks, if any, would holding the tournament without fans still pose to the athletes. Would you recommend canceling something like this altogether? Are there risks with the athletes that still play without fans?

MARC LIPSITCH: Probably there are some risks to the athletes. I mean, basketball is not rugby. It’s not quite as close contact. But there’s a lot of contact between people. And so I think it wouldn’t be risk-free, but I think it’s certainly a better approach than exposing huge numbers of people.

So I think — you know, I try to be emphatic when I think there’s really strong evidence of something. This is something where I don’t think there’s much evidence. But from basic reasoning, you would expect, if there’s a sick player or an infected player, they might transmit it to other players. But just on the numbers side, that’s less worrisome, although we care about each person, but we also care about the total numbers. And that’s less worrisome than risking transmission among hundreds of thousands or tens of thousands of spectators.

OPERATOR: We’ll take our next question.

Q: Hi. I was just wondering a couple of things about the testing. Do we have any sense whether early testing can tell anything, if somebody is not symptomatic, whether that can reveal anything? And also, whether people should get into treatment early, and if you have any thoughts about vaccination efforts. I’m interested in that, too. Thanks.

MARC LIPSITCH: I have not — there are a couple of peer-reviewed articles that I have just not had a chance to read about the timing of viral shedding, relative symptoms. I think they’re mostly after symptoms, rather than before, because not many tests have been done intensively before symptoms. So I think it’s hard to say, and that current levels of testing, even in places with a lot of tests, probably testing well-feeling people for their own good is not on — you might be able to do it as a surveillance measure, where you’re testing a sample of people to try to see what the prevalence in the population is, but to do it for patient care purposes I think is — we’re not ever going to have enough tests for that.

In terms of getting early treatment, you’re aware there aren’t any specific antiviral treatments. And I don’t think that there’s anything known about something else you could do early in the infection to improve the chances of a good outcome later in the infection. I’m not a physician, I should make that clear. So you should probably ask a physician. But I’m not aware of any data that says early treatment is beneficial, mostly because we don’t have specific kinds of treatments. Those are being tested, and potentially could come out in a matter of months if the tests are successful.

In terms of vaccines, as most of you are aware, there are something like two dozen efforts at least that are going on around the world, some more advanced than others. The estimates from the National Institutes of Health in this country have ranged between a year, a year and a half, or two years, depending on which day you hear them speaking, until there would be — until, in the best case, there would be widespread availability of vaccines.

The best case might not happen, for all sorts of reasons. It’s a challenging type of virus to make vaccines for, as evidenced by the fact that there was no vaccine for SARS or MERS, despite some efforts. The efforts have been ramped up a lot now that there’s a widespread infection. And hopefully, that will pay off. But I think vaccines are a long way off, unfortunately. And we need to plan for having them, but we shouldn’t assume that they are going to be available on a wide scale anytime soon.

Q: Thank you.

OPERATOR: We’ll take our next question.

Q: Hi. Thank you very much for doing this. I’d like to ask you two things. One is, I wonder if you have a sense of whether the pattern of severity of the cases in the United States mirrors what has been seen in other countries, I guess especially China, since they’ve had the most cases. And then my second question is, you said that the testing is one of a number of debacles. And so of course we’d like to know what else you consider a debacle. Thank you.

MARC LIPSITCH: Right. Perhaps I should have been a little more moderate in my language. But I think to answer the first question, I think the cases in China are unrepresentative because they were discovering the epidemic at the same time they were documenting it. And so severe cases got found, but at least they were testing a lot of people.

The cases in the U.S. are so unrepresentative because of the way they’ve been discovered that I think, even if I had all the data in front of me, I wouldn’t really know what to do with it because it’s just so haphazard what cases got seen and what cases didn’t get seen. I mean, I’m sure in the middle flu season for an elderly person to die of pneumonia in a hospital is not that unusual.

And so before people had the ability to test, and which is still the case in many places, there must have been deaths from this that just got missed in the United States because you couldn’t test, and nobody would have said this is so unusual that we must test it. I’m just guessing, but that happens in the winter. So that’s one thing.

In terms of debacles, maybe I should scale back the language. I think the lack of testing in the United States is a debacle. We’re supposed to be the best biomedical powerhouse in the world, and we’re unable to do something that almost every other country is doing on an orders of magnitude bigger scale, which essentially any graduate student could do. It’s not technologically hard. It’s hard to scale, but not hard enough to scale that any other country failed. So that one I would use the term debacle.

I think other things that are unfortunate are that we, in the United States, have spent so long denying the existence of cases and treating the numbers that come out as something meaningful, rather than as an indication of no testing. So that’s related to the testing problem, but it’s a matter of political will and interpretation. I think the early failure in China to acknowledge this as a human-to-human transmitted infection, which got fixed very quickly, but that was true for a while, was obviously tragic for the death of the doctor who blew the whistle, and also just lost us all time.

Maybe I’ll stop there, because I think it’s — I’m not sure what else to say, but I think the fact that we’re going to have the kind of pandemic that people have been preparing for for years sweep through the world and do so much damage, as it seems to be doing in Italy and Korea and China, and really not have a good solution is a sad commentary on the state of preparedness. But I’ll stop there.

OPERATOR: We’ll take our next question.

Q: Hi. I came into the call late. You might have answered this, but what is your best estimate for the number of cases out there in the U.S., given the gap in testing, and what is the best estimate you’ve seen for the doubling rate?

MARC LIPSITCH: I don’t really have a best estimate right now. It’s something I would like to focus on, but I’ve been trying to do many other things, and I just —I don’t have a good answer for that. I think it’s probably in the tens or hundreds of thousands. But it’s really hard to know. I mean, without good testing and hazard assessing, I just don’t want to venture a guess.

The doubling rate that I’ve seen in most cases is around five to seven days. The doubling time is five to seven days. There are some estimates that are higher — sorry, faster than that. And I need to sit down quietly with the papers and read them, because I haven’t sat down and done anything quietly for about a month now. So I don’t have an opinion yet on which of those are best.

OPERATOR: We’ll take our next question.

Q: Hi, Dr. Lipsitch. Thank you for talking to us. You’d mentioned the number of intensive care beds that were necessary in Wuhan in the highest day. And if I got it right, per person it’s equal to the number of beds that are available in the U.S. So I have two questions about that. First, what was the percentage of severe cases that needed intensive medical care in Wuhan?

And second, health care infrastructure is something that really worries us in Brazil. So we ask ourselves, will our health care system be able to respond to the challenge posed by COVID-19 or not. So what health care preparedness measures should be put in place, in your opinion? I mean, China built new hospitals. So it’s really difficult to do that, but should we have more intensive care beds? Should we have more ventilators? Should we open up rooms for COVID-19 patients? What do you think should be done?

MARC LIPSITCH: Yeah, that is not an area where I’m expert. I think maybe on a future call we should have somebody who’s more an expert on hospital preparedness, because I don’t have a — it’s just not my field. But I think all I can say is that, based on experience elsewhere, the demand will be high for intensive care.

I’m also going to deflect the question about the proportion of cases, because there are a lot of very precise definitions of severity. And in our preprint, which I will ask —I think Todd or Nicole must have a list of who’s on the call. And I’ll send that preprint out to link to the call. I don’t want to get the numbers wrong, and it will take me another 10 minutes to make sure I have it exactly right.

OPERATOR: We’ll take our next question.

Q: Hello. Thank you, Professor Lipsitch. Italian authorities closed schools, universities, cinema, and almost locked down an entire country. Do you think these measures can be effective, or were they implemented too late? And for how long they can be implemented? And what leads you to say that these measures are not sustainable for a long time?

Second question, you revised your estimation of what proportion of the adult population would be infected by the virus. Why did you revise it?

MARC LIPSITCH: OK. So the first one was about six questions. And I’ll try to answer them. I think the control measures in Italy will make a difference. They will not make an immediate difference to the strain on the health care system because of the reason I mentioned earlier, that infections today will become intensive care cases, some of them — obviously, most of them won’t but those that do, the intensive care problem in three weeks will be the people — or two weeks will be the people who are infected today.

So it’s going to be a delayed benefit. And hopefully people won’t lose heart and will keep the measures in place until the benefits can be seen. But they will be seen because less transmission means that the number of new cases will at least slow down, and hopefully start to go down in absolute terms. It depends on how efficient the measures are. But we’ve seen from China and also Korea that those measures can work to bring the absolute numbers down.

How long do they have to be kept in place? Unfortunately, it sort of relates to the last question. There’s no way the virus stops circulating except if environmental conditions change enough to stop it, which I don’t think is going to happen. And we can talk about seasonality if someone wants to. I don’t think that will be a major factor, and in any case, it will be a temporary factor if summer helps.

So either the environment has to change, which is unlikely, or enough people have to be immune to the virus so that each case makes less than one new case through contact. And if, as we believe, the basic reproductive number, which is the number of secondary cases per case at the beginning of the epidemic, if that number is around two, then that means around half the population has to be immune before new cases fail to take off into chains of transmission.

So it’s going to be a long time. And I think until we have a vaccine, the only really effective thing to do is to manage the problem by keeping interventions in place so that the number of new infections is something that the health care system can deal with. The long-term solution might be a vaccine, but as we discussed, that’s a long way off, probably.

The second question was about why I thought 20% to 60% of adults were likely to get infected throughout the epidemic, instead of 40% to 70%, as I said earlier. All these numbers obviously are quite uncertain. Both of those are large ranges, and they’re different large ranges. The reason why I reduced what I was saying is that early estimates of the contagiousness or the basic reproductive number were around 2.2 or a little higher, and more recent estimates seem to be a little bit under 2.

And the more contagious the virus, the more people have to get infected before transmission can end. And so as the data became more compelling that the transmission was perhaps less intense than we thought in an uncontrolled epidemic, so basically the number was lower than we thought, it seemed appropriate to lessen the expected number of cases.

And those are infections, not — sorry, those are infections, not cases. So — or not symptomatic cases. So it’s important to say that people have been imagining that the 1% or 2% or, by some estimates, 3% case fatality rate is applied to that percentage infected. But in fact, those case fatality rates are for symptomatic cases. And I think the best estimates are still around 1% to 2% of symptomatic cases ending up dead, whereas some cases will be very mildly symptomatic or not symptomatic, and wouldn’t be counted in the denominator. So it’s less bad than multiplication of 1.5% by 20%.

OPERATOR: We’ll take our next question.

Q: Hi, Marc. Thanks for doing this. Question kind of relating to the idea of herd immunity versus the vaccine. Is it possible in a place like China, which reported just 31 new cases yesterday, to turn the clock back to containment? In other words, to allow people to have few enough new cases that you can then allow people to go back to work and allow people to go to movies. Or are we kind of in this for the long haul?

MARC LIPSITCH: I think at some point, China is not going to be able to hold onto the extreme social distancing for the two years or more — maybe less, but for two years, if that’s the amount of time it takes to get a vaccine. So it clearly is going to have to loosen. And I saw a report this morning that Hubei province, where it started, is already starting to reopen some businesses.

And yes, if you have few enough cases, and you have very good testing and good public health systems, it is possible to do essentially what Hong Kong and Singapore are doing, as I understand it, which is to have some social distancing in place, not a complete shutdown, and then to manage the cases one by one. So when we talk about containment to mitigation, we might get back to containment, and China potentially could get back to containment, but it’s tricky because you risk getting out of control again.

So I think that is one option for a longer-term solution. It’s hard, and it requires more resources than some places have. And it will also require —I’m not sure if this is correct. I think I saw a report that China is now restricting travel from Italy, inward travel from Italy, because they have it under control and Italy doesn’t.

I’m not sure if that’s true, but whether it’s true or not, that is part of control strategy. If you have a country where you’re still counting cases or you’re back to counting cases again after an out-of-control period, then you have to start worrying about travelers, because travelers matter when your epidemic is small. They don’t matter when your epidemic is big, as much.

Q: Are we closer to walking down the path of Italy, or the path of Hong Kong or Singapore?

MARC LIPSITCH: I’m afraid we’re much closer to Italy because we have no sense of how many cases we have because we haven’t tested. So it’s not plausible that we are able to do containment right now.

And I would say also that certain health departments have been struggling with this. Sacramento decided a day or two ago that they would stop trying to track cases, and just move straight to mitigation as their only strategy. New York has, it’s been reported in the Times at least, and probably elsewhere, that New York is really struggling because the resources required for all the contact tracing are so intensive that other health department functions, including the mitigation functions, are being compromised.

So it’s a tradeoff. And I think it’s clear, at the very beginning, you do containment. When it’s out of control, you have to switch to mitigation because containment isn’t working and isn’t scalable. And then maybe you scale back to a combination of mitigation and containment if you get it back under control. And Hong Kong and Singapore may be the two places where it’s never really got out of control too much. And so they can sort of bubble along. But again, they have to keep it up, because if you let up, then the virus starts to spread again.

OPERATOR: We’ll take our next question.

Q: Hey, thanks for taking the call. In terms of what we understand about the mechanism of how the virus works, do we know anything about whether it’s extremely more contagious or more lethal than the normal seasonal viruses that circulate?

MARC LIPSITCH: I mean, I think the — I should know this because we have estimates that we submitted for publication, but they’re not in front of me, and my mind erases every morning when I wake up. So we do have estimates in our preprint of the — of our article on the five-year future of this virus for what the contagiousness of seasonal coronaviruses is, which could be compared to this. And I’m sorry, I’m just not able to —

Q: But I’ve been quite interested in hearing what we know about the mechanism of how it gets in the body and works. Like, do we know enough to know— 

MARC LIPSITCH: Yeah, nothing about the virus itself can tell you if it’s lethal. Only the virus in combination with the host, as observed in people. I mean, those are questions of epidemiology. There’s nothing about virology that can predict those with certainty. There’s a longstanding debate in flu virology about what are the determinants of contagiousness and lethality. And every time you make a rule, some new virus comes along that violates that rule. So that’s not productive — I mean, it’s a productive discussion and scientific inquiry, but there’s no clear answer. The gold standard for how lethal something is is how many people die of it, not whether —

Q: Just its track record.

MARC LIPSITCH: — there’s a certain receptor. Yeah.

Q: Right. OK, got it. OK, thank you.

OPERATOR: We’ll take our next question.

Q: Hi, Marc. Thanks for doing this. I don’t know whether this has been asked before or not because I jumped on late, but what’s your opinion of the discussion now about HIV drugs and malaria drugs to possibly help in this situation with any of these people who have contracted the virus?

MARC LIPSITCH: I am not an expert in that, and I don’t know anything more than has been reported. I probably know less than has been reported, because I don’t have time to read. I think there are reasons from laboratory studies to suggest that they may be useful. And the only way to find out is testing them. And that’s underway for a number of them. But as I say, I don’t have any more details than are in the press.

OPERATOR: We’ll take our next question.

Q: Hi. Talk to us a little bit, if you would, about the timing. When we talk about social distancing, when we talk about closing movie theaters and canceling events, are we saying that that’s got to happen for two years until there’s a vaccine, or what is the long-term — can we look out a couple of months and see what — is there going to be a change in this potentially?

MARC LIPSITCH: I think that is obviously an unsustainable, or fairly obviously an unsustainable scenario. And so I think the immediate goal of doing all of that is to avert Italy and Wuhan’s problems of overloaded hospitals. Once we achieve that, either before it happens or get through it after it happens, then I think it’s going to be kind of a matter of putting on the brakes as hard as we can, and then figuring out and watching from places around the world how much can you let up on the brakes and still have a functioning health care system, which is a pretty grim way to think about, but I don’t actually know any other solution.

I mean, China has shown that you can more than stop the epidemic, meaning they really went down quite dramatically in many cities with very extreme measures. So I think China will begin the experiment of, OK, now if we open some businesses, what happens. And so I think, as other countries have this experience, we will all be watching to try to figure out how little disruption can you get away with and still have a functioning health care system.

OPERATOR: We’ll take our last question.

Q: Hi. Thanks. While we’ve been on this call, the WHO has now declared this a pandemic. So you know, before we all get off, I just wanted to ask you if you think that’s the appropriate move now, and does it change anything at this point. And if so, what would it change?

MARC LIPSITCH: Oh, they did. Ah.

Q: Yes, they have just like five minutes ago declared it a pandemic.

MARC LIPSITCH: Huh. OK. That’s news to me. I don’t know. I mean, I hope that it adds urgency to efforts to mitigate it, because those efforts need urgency. I think the scientists have been calling it a pandemic for a long time, or many scientists have been calling it a pandemic for a long time. It’s good that the World Health Organization is saying that, and it is appropriate for them to be a bit more cautious.

I mean, I think there’s a general issue that public organizations need to stick closer to the data than — and by that, I mean governments and the World Health Organization need to stick closer to the data, and people like scientists, who are independent, are more free to speculate about what they think the data mean. I think my ideal would be that we need in the middle. And we actually wrote a paper — Mauricio Santillana — last year recommending that, that public organizations report their interpretations of the data, along with the data themselves, so that people can understand what the data mean.

But I think there is an appropriate level of caution by governments and WHO to state things when they’re absolutely sure of them, while people like me are free to state what we think is the best estimate. And I think those are both important roles. So I don’t fault them for being cautious. I think I might have gone a little sooner than this, but I’m glad that they have said that.

This concludes the Wednesday, March 11th press conference. 

Press conference with Marc Lipsitch, professor of epidemiology and director of the Center for Communicable Disease Dynamics (March 4, 2020)

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