You’re listening to a press conference from the Harvard T.H. Chan School of Public Health with Bill Hanage, associate professor of epidemiology. This call was recorded at 11:30 AM Eastern time on Tuesday, March 31.
Previous press conferences are linked at the bottom of this transcript.
BILL HANAGE: Good morning, everyone. I am professionally William, but you can call me Bill if you like. The only people who call me William are my mother and ex-girlfriend.
I’m going to start with a couple minutes here on the development of the last few days nationally and globally. And I actually recognize you know a lot of this, but I think it bears repeating.
The United States has the largest number of COVID cases in the world at more than 160,000. That’s more than 60,000 more than Italy. Now this not only [AUDIO OUT] population size. [AUDIO OUT] also a major change in the landscape of testing. The WHO has recommended that 10% tests coming back positive is an indicator of a sufficient surveillance state, or state of surveillance.
Now many states in the US have achieved this milestone, with some exceptions. Notably, California appears to still be struggling with about a 23% positive rate. Now while tests are rare, they do need to be concentrated on the place where they need it most, which is people who are receiving treatment in order to ensure that they are appropriately treated and the health care workers use appropriate personal protective equipment. Health care workers should also be tested.
Now these changes are welcome. But us epidemiologists desperately need more data on the characteristics of the patients being tested in order to understand the cause of disease. And this is going to be needed to be collected on the front line. Now moving to that front line, we are in the early stages of outbreaks in metropolitan areas across the country. These are not all at the same stage due to the outsized consequences of early events like Mardi Gras, which likely initiated many transmission chains.
Now these differences are hard to assess due to local differences in testing, among other things, historically. But we should expect growth everywhere. At present, the doubling time is about four days, although that may depend a little bit more on the testing, the increased rates of testing, as I said. And I would note that smaller communities are expected to show considerable variation as a result of random variation in how many introductions they’ve seen already.
Now where it is taking place, physical distancing is hopefully already slowing the rate of new cases. But the benefit will not be seen for some time, and I’ll illustrate that with a global comparison. Italy seems to be reporting a slowdown in new cases. There were around 4,000 yesterday, which was down from the day before.
Now for reference, at least stronger measures were enacted on March 7 in Lombardy, the most severely affected northern region, and two days later for the rest of the country. So, based on this, and with reference to Wuhan, we should not expect to see the benefit that we hope to get for three weeks or more. And with that, I will hand over to you, and I’ll take your questions.
MODERATOR: All right. Looks like we have our first question.
Q: Yeah. Hi. Thanks very much for doing this call. I’m curious – this maybe sound very premature, but I’m wondering if you could kind of walk us through what you see the endgame for this being. Like how are we going to put this thing back in the bottle?
BILL HANAGE: Now that is obviously a very big question which a lot of people want to know the answer to. And I’m going to preface my answer by saying that given the state of scientific knowledge, what I have to say now can only be distinguished as speculation.
I think that our major focus should be the first wave, which is going to be happening over the next couple months. And once we have dealt with that, the consequences will really depend on things including the extent of health care that has been built up during the first wave, the amount of population level immunity that has been built up during the first wave, and anything that we have learned from it in the ability to rapidly isolate and deal with future outbreaks.
I think that one of the things which may be important is repeated rounds of physical distancing such that we relax things, and then we are able to reinstate them at a point when we notice that the rates of transmission are starting to increase again because in the absence of a vaccine, the only way we are going to be able to slow this down is by population level immunity. And we need to find the safest way in which to do that.
Q: So, I heard some folks saying that the vaccine is obviously quite a ways off. Is the level of immunity that we’re seeing so far from patients – any estimates on where you get herd immunity? There’s been some reports of repeat infections. Has anybody been able to do the modeling to figure out how many people have to be infected already in a community to provide enough for herd immunity?
BILL HANAGE: OK. Sorry about that delay. I was just unmuting myself. So, the herd immunity [INAUDIBLE] calculation, you can estimate the sort of fraction of the population that would need to have vaccinated in order to prevent outbreaks to bring the reproductive number below one, the effective reproductive number, that is. And it’s between 50% and 70% given current estimates.
Now that is assuming that infection does result in immunity. And we do see signs of immunity, but we don’t know how effective it is or how long it will last. Now to reinfections, it is not clear how many reinfections are occurring, largely due to the fact that testing is not always perfectly sensitive. So, some of those cases you’re seeing where it looks as if a person was testing positive, positive, negative, and then later tested positive again, may be likely explained by one of the intermediate tests just not picking it up when it was there.
Now the amount of that that’s happening we don’t really know. I think, and I would make the point, that at this stage of the outbreak and of the pandemic, it’s been hard enough managing to identify those people who are infected once. So, it’s going to take a while before we can be secure about who’s been infected twice.
MODERATOR: Next question.
Q: Hi, Bill. I wanted to ask if – there are some reports in Russia that doctors found a correlation between mandatory tuberculosis vaccine and the amount of deaths. Is that something that Russia can speculate about, or there is an actual medical base behind that?
BILL HANAGE: That’s an interesting question. I think it’s too preliminary to make a deep pronouncement on it. I mean, the BCG vaccine does seem to have a number of interesting immunological effects. At this stage, it’s way too premature to stay because you will see a lot of reports which are saying so-and-so has been less affected by the coronavirus pandemic. And I think all such reports should add the words, ‘so far’ at the end of that kind of sentence.
Q: Thank you.
MODERATOR: And the next question?
Q: Hello. So, William, I have two questions. One, you mentioned that we may have to have several rounds of physical isolation. Do you actually see the scenario where we may have the stay at home directives lifted and then re-imposed again in the future? That’s my first question. My second question, is what are your thoughts on the discussion around community masking?
BILL HANAGE: Thanks. So, to take the first one, yes, I do think that it is possible it will be lifted and then reinstated again. It will not happen in the same way. I think, for a start, that there will be much more likely to be buy-in as a result of the consequences of the first wave. In fact, after what happens over the next month or so, it may be quite difficult to encourage people to be returning to normal.
Now as to the question of community masking, my own views are in something of a state of flux because we have usually taken the view that masks are not effective and potentially risky. Obviously, at the current state, you should be concentrating masks for health care workers because there are shortages and health care workers need more than anyone.
However, assuming that masks are available for use in the community, they could serve an important role. And that important role is not in preventing you becoming infected. The role is in stopping you transmitting if you are infectious because the whole idea behind physical distancing and the reason that it works is that if you yourself assume that you might be infected and try to avoid infecting others, then that has a real public health benefit.
Masks, we know from studies, the kind of masks that people typically use are not effective necessarily at preventing acquisition of disease unless they’re a special type of mask. But they may help protect people who are infectious transmitting. And if there is a large proportion of people who are mostly asymptomatic, then they could have an outsized role.
Now I will point out at this stage that this should be caveated with the fact that we know that people who wear masks tend to touch their faces more. And given that touching your face is a potential route of transmission, we would have to figure out whether or not the benefit that comes from preventing transmission from infected individuals was not outweighed by that of people touching their face more.
MODERATOR: OK. And the next question?
Q: Hi, Bill. I wonder if you could comment on the estimates that are out about 100,000 to 200,000 possible deaths here in the US. Do those numbers seem reasonable to you, high or low?
BILL HANAGE: So, I think that at the moment, I’m not going to get caught into very specific estimates of exactly how many deaths there are. They certainly seem within the reasonable framework. I would not be particularly surprised by them. I wouldn’t be particularly surprised if they were higher. I wouldn’t be especially surprised if they were lower.
One of the things which is difficult for those of us who have been involved in modeling this is in communicating the amounts of uncertainty that we have. Now you can get quite different results with a few different assumptions. And you’ve noticed people asking questions over the last month or so which are very good questions about things like how many asymptomatics are there, because know that will determine a great deal how many deaths you get because it determines how many people are already immune and who aren’t going to be able to prevent spread to others.
Now against that, we have the observations that we have got from Wuhan, Italy, Spain, and now New York City. And I tend to think that our focus immediately ought to be on that situation. And while the numbers we’ve been talking about are entirely plausible, I think that it would be wrong to get tied up in specifics at this stage.
Q: Do we have a better sense at all about the number of asymptomatic cases?
BILL HANAGE: That’s a great question. So there has been a study which came out of one of the Washington sort of elder care homes, senior care homes, which sampled people fairly carefully. And of the people they identified as being infected, I think 50% of them were asymptomatic or presymptomatic at the time of testing.
Now I want to point out, again, caveats around asymptomatic, presymptomatic, and so on. Just because somebody doesn’t have symptoms now, it doesn’t mean that they are not going to develop symptoms. Now we have known that asymptomatic transmission or presymptomatic transmission is possible for some time. But we still– and this is a crucial distinction– we still do not know exactly how much it is contributing to the course of the pandemic. Just because something is possible doesn’t mean that it’s a dominant mechanism. Does that help?
Q: Yeah. Is the 50% – that seems really high to me.
BILL HANAGE: Yeah. I would emphasize it’s only one report. It’s NMWR and it came out, I think, a couple of days ago.
Q: Terrific. Thank you.
Q: I’m wondering if you could comment on sort of the next phase of controlling this pandemic, assuming we sort of flatten the curve and get cases under control. Do you think that the kinds of technological tools used in South Korea, like using phone data to do contact tracing, are necessary to have a robust enough contact tracing system to use that and widespread testing as an alternative to periodic social distancing? And is something like that feasible in the US?
BILL HANAGE: That’s a very good question. And I’m going to make the point at this stage, which is sort of fairly obvious, is that when it comes down to this – I’m speaking as an epidemiologist – I recognize that the things we’re talking about have consequences for things like civil liberties.
So, the types of digital approaches which have been pioneered elsewhere do seem to be effective when you’re talking about the situation of attempting to prevent invasion by reintroduction from elsewhere, outbreaks and fighting containment and contact tracing.
There is another potential use for those kinds of data, which are taking it – I can hear a cat. That’s awesome. There are other potential uses for such data. If you put them in aggregate, then we can gain, I think, information about the types of areas where there have been a large amount of movement and maybe link that up to other indicators of disease activity, which could provide targeted social distancing advice.
But I think that there is likely to be a digital role for this, and when it comes in, it should be done, obviously, with consent.
MODERATOR: The next question?
Q: Hi. Thanks so much for taking the question. So, the state-by-state statistical model from Christopher Murray in Washington has gotten some particular attention at recent White House briefings. I’m wondering if you had any thoughts on any advantages or disadvantage of that model based on the methodology or its assumption, if they’re independently or relative to other approaches, for example, like the mechanistic approaches we’ve seen from Imperial.
BILL HANAGE: Again, that’s a great question. There’s a big difference between the sort of statistical model which we’ve seen coming out, which you’re referring to there, and the mechanistic approaches which have been used by the Imperial Group.
Now the comment that I will make on Chris Murray’s model is that it makes some very strong assumptions about the effectiveness or otherwise of various different elements of physical distancing. It is, in my view, excessively positive on our ability to achieve Wuhan-style quantities of shutdown. As a result of that, it is, I would say, tending on the side of the optimistic when it comes to burden on health care.
Now that can be changed, obviously. It could be modified. And if you’ve actually been examining it over time, you will note that quite a lot of the estimates have been being updated markedly as things have happened and facts have emerged on the ground, and it has become clearer that things are happening at a pace which is more rapid than they were initially thinking.
The other comment I will make is that it is extremely difficult to get secure numbers on this. Numbers are still quite small in places, and they tend to be concentrated towards severe cases, and in this case and others, deaths. And if you’re dealing with small numbers, then the uncertainty gets a lot larger.
So, I would be very cautious. I’d be cautious about taking any model in isolation. I would always want to consider a number of different things alongside each other. And I would focus, again, my point upon the fact that based on all of the evidence we have from other places, we are going to be facing a very difficult situation very shortly. And it would be prudent to adopt a precautionary principle when it comes to thinking about how to respond to this. I hope that helps.
Q: It does. Thank you very much.
MODERATOR: The next question.
Q: Hi there. Thank you so much for taking my question. I’d love to ask a little bit about testing. We’ve been seeing a bunch of new tests come on the market in recent weeks, and some promising very quick results for a point of care test.
Kind of two questions in one. Have these tests help to relieve the shortage we were previously experiencing? And what are your thoughts on having so many tests out there? Is this a good thing? Are there any downsides?
BILL HANAGE: Again, that’s a great question. Obviously, we have been wanting more testing. And I, among others, have been kind of vocal in saying we need more testing. The availability of new kits is welcome. But it produces a problem of its own, which is that they’re not necessarily all alike.
If you think about it, it’s kind of straightforward to see that you can have many different tests. Even just using the same test, you could have the question of do you take one swab? Do you take swabs from different locations? How do you use it? And so, this lack of consistency is going to create noise in the data. And we’re going to have to figure out how to deal with that.
There is also the fact that a number of these tests are apparently – it’s very difficult to be absolutely sure without really robust investigations how sensitive they are because there are some cases I know of in which people have generated tests, and then sometimes people have bought tests, and it’s turned out that they are only able to detect about a relatively small fraction of true cases.
So, the fact that there are lot of tests is good. What we still want to have is more data on which are the best tests, and then we want to ramp them up and get them out to as many people as possible.
MODERATOR: The next question.
Q: Hi. Thank you. I missed the very beginning so I apologize if you already addressed this. But I want to talk a little more about how the virus is transmitted. There was a lot of talk in the beginning about these are droplets that go out six feet and then fall to the ground. But it really seems to me – and it would explain why it has been transmitted so quickly – that there must be airborne transmission. And I guess there was a study out last week talking about that. What is your view? Is this virus airborne, and does that have any implications for the utility of wearing masks?
BILL HANAGE: Thank you. So, the first thing I’m going to say is that I’m basing what I’m saying here on the investigation the WHO China mission did. And they only found evidence for droplet and fomite transmission, but they could not find evidence for airborne transmission.
Q: Can you clarify the distinction?
BILL HANAGE: Yes. Certainly. So, fomites are things which are picked up from surfaces which can be left there either by people coughing on their hands, touching their hands, contaminating the surface, or indeed, coughing onto the surface. Droplets are these small bubbles of fluid which can carry virus which are emitted by coughing, sneezing, or indeed talking. And airborne or aerosol transmission are smaller particles in the air which can hang around much longer.
Now the airborne transmission is associated with diseases like measles, which have a much, much higher reproductive number than this. Now we don’t have very solid evidence for airborne transmission at the moment. While there was a study – I think it’s from the University of Nebraska Medical Center – which did find that it could detect viral particles in the air of patients’ rooms, those viral particles were not viable, which means that they could not be grown and they would not have been infectious. And this is in contrast with what was found on surfaces.
Now when people talk about droplets and the six feet rule, I think it’s important for the public to understand that it’s not that they will always fall to the ground exactly six feet. It’s not like they come out to here and then they hit a magic force field six feet away and suddenly fall to the ground. Instead, that’s like the area where you would typically expect them to be falling to the ground. And when it comes to the recommendation to keep more than six feet apart, it’s really important to recognize that this is not necessarily about wholly eliminating transmission. It’s about reducing it.
And it’s not that there is absolutely zero risk. However, it is a greatly reduced risk of what there would be, in particular if you were in large gatherings with large numbers of people. So, I still think that I have not seen evidence to convince me yet that there is an airborne mode of transmission here. However, I obviously think that we are still learning a lot more about this virus.
Q: But is there a real difference between droplets and tiny droplets that can float on the air for greater distances?
BILL HANAGE: No, it’s the size of the droplets. The larger droplets tend to drop more quickly than the other ones. I mean, if you think about the situation with measles, just to give you some sort of epidemiological context, the reproductive number of this, which is the number of new cases you’d expect if you were to drop it into a completely susceptible, well-mixed population, is between 2, or maybe 3.5, possibly a little higher in some contexts, possibly a little lower depending on the contact structure.
Now for measles, which is airborne transmission, that number is 18. So airborne transmission can really do some very, very, very rapid spread. And at the moment, the investigations of this suggest that the reproductive number, while quite enough in order to produce a very major problem, is not at that scale.
Q: But if we’re seeing transmission by people who aren’t yet coughing or sneezing – and I’m also thinking that choir in Los Angeles where a lot of people get sick just by singing – it suggested it’s something different than with the flu, that it’s really, really tiny particles that you’re breathing out, right?
BILL HANAGE: People singing are going to produce a lot of droplets. And if they’re standing close together, then they’ll be producing lots of droplets and they will be landing on each other. And when you’re singing, you tend to breathe deeply. So, it’s entirely reasonable to think that transmission could be achieved by droplet mechanism within a context like that.
Q: I want to get one more question and then I’ll yield. But can you talk a little more about the difference between asymptomatic and presymptomatic? Do we think that most of what people are calling asymptomatic may actually be presymptomatic, people who are about to get sick? Is that the more likely scenario?
BILL HANAGE: Great question. The true rates of asymptomatics are very, very, very difficult to tell because mostly we don’t test for them. And it’s obvious that we are– at the moment, like I said, when tests are scarce, they need to be concentrated at the place of greatest clinical need.
Now you may be interested to look at a study which has just been coming out of Iceland. Iceland has managed to test, I think, 3% of its entire population already. And the cases that are identified there are going to be a much better picture of the true nature of what’s going on in the population.
The caveat I will add to that, though, about the question of is it asymptomatic or presymptomatic, is it in order to be absolutely sure that it is asymptomatic and it is not going to become symptomatic, you need to follow people for a fairly long period of time. And we don’t necessarily have enough data yet to be able to say where are we with that.
I will make the comment that I have personally seen people with abnormal chest CT who have displayed very few, if any, symptoms and whose infection has then resolved. Now that indicates a pathological process, but it wouldn’t be detectable by anybody who wasn’t doing a chest CT.
And I will come back to what I said earlier, that the fact that those exist does not mean that they transmit. But again, we need to get a handle on things like that. And the more data we can collect, the better.
MODERATOR: The next question.
Q: Hello. So I am interested in this question of now that we’re in this phase of trying to lift the critical care capacity of the health care system to care for the very sick – and that’s where we have the potential to save a lot of lives, as well as just continuing with social distancing – I’m wondering if you could say a few words about how the general public can potentially help support the health care system at this time because it does seem like a lot of it is up to hospital leaders and the federal government. But what role do you see for the general public in supporting the hospitals caring for the sickest in this time?
BILL HANAGE: So possibly the best thing that can be done is preventing becoming infected yourself so you don’t enter care and end up presenting a risk to yourself, or indeed to others. But I think a lot of people know that. And you can look to see if your local hospitals are looking for donations. And that could be donations of multiple things. If you have been hoarding masks, you should send them to your local hospital. And when I say this, I mean your local hospital. I do happen to know of a few places, some big-name hospitals who shall still remain nameless, have received a huge number of donations, whereas others that are equally deserving but are not as famous have been struggling. So, do look to see if you can make donations either of masks, or if you have the money, financial donations to your local hospital.
I also feel that this is a moment for people to come together. And this is me speaking personally rather than as a representative of CCDD or Harvard. But every night at 8:00, my family have been going to the door, opening it, and spending a few moments applauding the health care workers in our own community who are working so hard for us.
And we’ve heard a few people clapping back, but not very many so far. And I think that anything that we can do to recognize that we’re all in this together, and to support the people who are most at risk in the front line, would be really, really great.
MODERATOR: The next question.
Q: Hi, professor. You said that you are focused on the dynamics of transmission. And can you tell us more about it, why you want to study the dynamics of transmission, and what’s the challenge about it? Thank you.
BILL HANAGE: So, the dynamics of transmission are determined by things like how many people are infected by a case, and then how quickly they do it. And by understanding things like that, we can start to get a handle on questions like how many people have to be immune to stop new infections happening, how effective would a vaccine have to be, what can we expect in the near future, and what are the likely consequences of various different strategies?
Now in studying that, you examine very carefully the data as they come in. And then you attempt to understand which combinations of properties of the infection, in terms of the time between subsequent infections and how many people, on average, get infected by each person who is infectious. You put them together and you try and come up with a model that can explain those dynamics [INAUDIBLE] over time.
Once you have that model, which is the kind of mechanistic model that we were talking about earlier, then you can start to investigate the impact of various different other properties of the infection, like the case fatality rate. And then you can start figuring out how many people you expect to die, where the resources are, and so on – where the resources should be placed, and so on.
Now what is very difficult in this is that ordinarily, when you are studying an outbreak, you have quite a lot of data on those things and you’re able to nail them down into a particular sort of area of likely properties. Now with this pandemic, the challenge has been that while we can say some fairly general things about it, it’s very, very hard to know the specifics.
For instance, there’s the question of how much children contribute to transmission. We don’t have a very good handle on that. We know they don’t get severe disease, but we don’t know how much they contribute to transmission. And yet people have to make decisions before those data are available. And the role of dynamics in understanding modeling is to try and give people the best advice about what we expect to be happening to the disease in the population in the future, and to understand what we might expect in different places and at different times.
Q: One more question. You used to say that it’s very strange for what happened in Japan. And can you tell us more about it? So, do you approve their strategy, or what will happen next to this country?
BILL HANAGE: So, when I said Japan is very strange, what I mean is that the epidemic curves in most other places – at least places that are not like Singapore or Taiwan, and have been doing very, very strong, engaged activities to do contact tracing and containment – Japan has not done that, and yet its epidemic curve has been much, much sort of gentler. And it had cases very early on. Some of the earliest exported cases from Wuhan were in Japan.
Now I do not know why that is. Obviously, the Japanese situation is extremely different from elsewhere. But the reasons for it could only be speculation, so I’m not going to go there. However, recent upticks in and around Tokyo have made people more concerned about Japan.
So, I will return you to what I said earlier, that at the moment, every time we are talking about places being more or less affected, we have to say perhaps it’s just that they haven’t been severely affected yet.
Q: And you said you haven’t been to Japan, but you just came from Israel. So, can you tell us more on the situation there?
BILL HANAGE: So yeah. I was in Israel a few weeks ago. And given how quickly this is changing, I don’t think I can say much about what the situation is like there now. I’ll make the comment that when I was there, they had an isolation unit that they had thrown together in 48 hours and which had excellent infection control with a green zone, a yellow zone, and a red zone and all of those good things. And they were preparing to be doing safe swabbing of large numbers of patients.
And I think that this shows the importance of preparation. But I cannot comment on what Israel is doing at the moment because as I say, it’s been about three weeks since I was there, and a lot can change in three weeks.
MODERATOR: The next question.
Q: Appreciate you doing the call. I was just wondering whether you have a sense as to whether Florida, particularly south Florida, could emerge as a hot spot in this epidemic. And also, are there any particular metro areas in the United States that you’re worried about?
BILL HANAGE: I’m worried about all metro areas in the United States. The potential for Florida is something which is beginning to raise concern because of the limited physical distancing which has been happening there, but also, I would say, the relative age structure of the population.
Now this is, again, the type of – I always try to distinguish between the things I know, the things that I am saying I believe are possible based on my knowledge and previous experience and expertise, and things which are speculation. So, this is in the middle category. If you look at Italy, and in particular the Lombardy regions, which have borne the brunt of the pandemic so far, they have a relatively older population who have a lot of contact with each other.
And given that at least parts of Florida are similar, I would be quite anxious about the potential for rapid spread in Florida. At present, as I say, we’re at relatively early stages in the epidemic curve. And it’s difficult to know where it’s going to be going. But I will be keeping an eye on Florida.
This concludes the March 31 press conference.
Howard Koh, Harvey V. Fineberg Professor of Public Health Leadership (March 30, 2020)