You’re listening to a press conference from the Harvard T.H. Chan School of Public Health with Michael Mina, assistant professor of epidemiology. This call was recorded at 11:30 am Eastern Time on Friday, April 17.
Previous press conferences are linked at the bottom of this transcript.
MICHAEL MINA: Alright, so just for anyone who I haven’t spoken to at this point, I’m in the Department of Epidemiology where I study infectious disease dynamics and transmission of viruses. I’m also in the Department of Immunology, so a lot of my research focuses on how viruses impact on the immune signatures of people, and to do that we developed a lot of serological tests, very, very high throughput serological tests, that are not for clinical use.
And then I’m also one of the medical directors at Brigham and Women’s Hospital, where I oversee portions of molecular biology diagnostics in the clinical lab there, and also at the Broad Institute, where we’ve had an ongoing effort to bring high throughput testing capacity to Massachusetts and New England more broadly. And now of course, we’re moving into the whole serology testing phase of this epidemic. And so, a lot of the efforts and interest have gone into serology more recently, now that the PCR viral testing is sort of doing its thing, if you will. So, I’m happy to take any questions.
MODERATOR: Thank you, Dr. Mina. Alright, it looks like we have our first question.
Q: Hi, Michael. Thanks for doing this and taking our questions. Let’s say the Commissioner of the NBA calls you and proposes the following scenario: in mid-June, the NBA would like to resume the season at Walt Disney World in Orlando. 500 or so players, and the additional team staff, call it 1,000 people. No one else at the facility for one to two months. Putting aside the security concerns and the feasibility of keeping it fully quarantined, the Commission wants to ensure that every individual is tested and cleared before entering the so-called quarantine bubble.
How would you advise them on testing for such a proposal and what sort of options were the NBA have at their disposal, presuming they have the financial means to purchase the testing equipment? Is the quick Abbott test everyone’s hearing about efficient enough, or is it best to go to a lab route? And how many retests would you need to feel confident there are no false negatives in the population? Thank you.
MICHAEL MINA: Are there going to be audience members as well or spectators? Is it just the players?
Q: Just players and the staff. So, it’s some small broadcasting for TV, but basically bare bones staff and players.
MICHAEL MINA: Sure. So, it’s a great question, and it’s one that’s obviously coming up a lot. I think that what would have to be done – the Abbott test might be okay, but I think really to ensure that everyone is staying safe, you probably want something, for example, to have if the teams are obviously going to be practicing. If they’re playing games, then they’re going to be practicing on a daily basis.
So first off, I would ensure that sort of on a daily basis teams have access to potentially even daily nasal swabs. They wouldn’t be in a position where they can have an outbreak happen on their team, so they would probably want to be doing nasal swabs on a daily basis. And you can use these more anterior narrow ones that are now coming about. And you could potentially have the Abbott ID NOWS maybe with each team. But you might also think about a pooled approach where you can use a cepheid cartridge-based assay or something, where you can pool everyone’s samples together on a daily basis and just run one PC assay. And if it’s positive, then you have to kind of pull it all apart and figure out who is the positive person. But that’s the kind of level of surveillance I think would really be needed to ensure that the teams don’t sort of blow up in the middle of the season.
And then I think that as the games start progressing, you probably would really need to have some way to very quickly be able to determine who’s positive and who’s negative, or just really positive on game day, if you will. And I think that that would require also having some sort of very rapid ability to test a lot of people quickly and, in that case, what I might suggest is, you know, assuming money is not an issue, these teams might want to consider investing in a portable lab. Essentially, you know, you could go at the Abbott ID NOW. They’re not actually as fast and reliable, potentially, and they’re not parallelizable. They have to be done in serial, so, you can’t get through a ton of people too easily.
But, if you have a little portable laboratory that you can put inside of a trailer or something like that, outside of a stadium or inside of a stadium, I could see actually having a higher throughput instrument that’s sort of a more conventional PCR right there and just swapping everyone as they come in and you’ll have results back in an hour. So, that’s the level that I think you’d have to be at in order to make sure that everyone’s safe and you’re not starting big outbreaks amongst the teams.
Q: Thanks. And is it that – do they have enough access to those supplies or is there a shortage of those tests and would they have to get in line, so to speak for the front lines at hospitals, etc?
MICHAEL MINA: I guess it depends on how much money they have. I would say that right now most of the reagents are still quite limited. Abbott, in particular, I think is quite limited, in even just the instrumentation that’s needed to run the Alere. Abbott purchased Alere and that’s the instrument that they use. Those I don’t think are really readily available to huge numbers, even if you want to pay for it.
But that’s where I think if you have a mobile lab type of thing, you can actually set up a more conventional real time PCR type of assay where you can buy more bulk reagents and, sort of, what we do at the Broad here, to do it in very high throughput. You can actually do this even in lower throughput, a few hundred at a time. And you don’t have to be purchasing from Roche or Abbott, you go straight to the source, to ThermoFisher, one of these companies, and you just buy bulk reagents and you can do it.
So, I think it can be done. You maybe have to have a PhD-level molecular biologist on your team to carry forward, but they’re not particularly hard if you have somebody who knows what they’re doing.
MODERATOR: Okay, next question.
Q: Hi. Thanks. I want to ask about the White House plan put out last night. It did not seem to have – you know, it mentioned testing, but it didn’t have any kind of numbers we need to reach this level of tests before we can reopen or anything like that. So, I mean, did you view that as a maybe a weak spot of the plan? Do you think we need a lot more testing before we can start going through that phase reopening that it envisions?
And the other thing was that Deborah Birx mentioned that she thought there was unused capacity. She said there’s like a million tests that could be done right now that aren’t being done because there are machines just sitting in labs that aren’t being used. I wonder if you think that’s accurate or is that an exaggeration, because maybe they don’t have the swabs, or they don’t have other supplies to be able to use those machines?
MICHAEL MINA: Yeah, so I think the question about how many tests need to be performed is a very difficult question to ask, and it really comes down to there’s two different types of tests. Now, there’s the viral PCR is and there’s the serology. I think doing sort of blanket PCR across the population isn’t really the way to go here. It doesn’t – even if you were to test everyone today, test every single person in the country today, you’d only be able to do so much with that information because there’s going to be a lot of people who are negative today that are going to turn positive tomorrow. And a lot of people who are positive yesterday who are negative today.
So, this is a transient virus, which limits the utility of using the viral PCR as a real sort of broad surveillance tool. It’s good if you’re doing contact tracing and want to find out who is positive and you have some evidence to think that you’re trecking down the right path. Serology, on the other hand, is very good and it’s a way to find gaps in immunity at the population level to know sort of where there might be a whole population of people who either have or have not already seen this infection. And you can make educated decisions about how to further monitor those people in the future. If they’re all susceptible, then maybe you want to put more resources into ensuring that you detect an outbreak early. And if they’ve all seen the virus before, then maybe you can relax in that sort of neighborhood or something, and not be worried about there being an enormous outbreak.
So, I think surveillance using serological testing can get us really far and it will also give us the baseline sort of number of sero-prevalence that we really need to better understand the virus that we’re dealing with. And then the other question that you asked was – what was it?
Q: Dr. Birx was saying there’s like a million tests that could be done using existing machines that just aren’t being used, but is that a supply issue or what?
MICHAEL MINA: That’s very much a supply issue. I can tell you that there’s still very many people in this country who would love to get viral PCR tests performed. There’s a tremendous number of doctors who want to get PCR tests. I was just on the phone just the other day with a very large hospital group that has over a million people in their network and really have almost no access to testing.
And this isn’t for a lack of the actual capacity to run the tests. In many parts of the country, it still will be delays to get testing performed but we actually have still some excess capacity for example at the Broad. It’s starting to get filled in now that that we’re doing a lot more surveillance, but there has been a bit of excess capacity across Massachusetts. And the real bottleneck has been actually these swabs and that’s been a story for a couple of weeks now. And it’s the swabs, and the media to put those swabs in. It’s just astounding, you know, these are still causing the problems and now it’s more the media than the swabs.
So, I would say while Deborah might be able to say that there’s a lot of excess capacity, we would have to take the whole thing into account. The machine that runs it is only part of the equation. And I think having a full plan for the whole country, you know, includes all of these up front, things like how to get the sample out of a person.
And so, I would say, while the instruments might be sitting – some of them might be sitting idle – that’s not the same as saying these things just aren’t being used. There is a tremendous desire and demand for tests, and people are truly, you know, clamoring to get any line on, you know, a swab producer or manufacturer, or the matrix that the swabs go into. And that’s become a very odd and difficult issue. And we’ve been we’ve actually been in touch directly with manufacturers in China to get crates of swabs put onto planes for us and brought here. And then there’s problems in customs, where we have tests or swabs sort of sitting, you know, in customs for a week. So, there’s been a lot of problems, I would say, and the testing is part of that, but it’s really actually a lot of materials now.
MODERATOR: Next question.
Q: Hi, thank you for taking questions. I guess I’ll just circle back on the last one, real quickly. You know, we seem to have plateaued at about, you know, this testing rate of, you know, 140, 150 tests per day. I mean, in your opinion, is that capacity enough anywhere in the country to safely begin testing what the Trump administration is suggesting, easing the social distancing guidelines, beginning to open up parts of the economy, or does testing still have to ramp up more?
MICHAEL MINA: I think it needs to become more widely available for sure. And some of that is these materials, I think. I mean, first off, I don’t think we should be – no, I would not be in favor of opening anything up until, you know, at least another from now or so. We really want to see that this virus has had weeks, met numerous weeks of decline. And even then, another number of weeks of really being very, very low transmission across the country before we can really realistically plan to open up without igniting new outbreaks but PCR testing is only going to be a part of that equation once things start to open up.
I think part of the benefit of getting serological testing available is going to be that we can actually know what fraction of the population has already been exposed, and that will tell us a lot about other aspects of this virus light in terms of its lethality and having a better denominator worked out.
But the testing, I think we’re really entering into this era of antibody testing and we’re not anywhere close to where we need to be. I think we’re going to see something with antibodies and the demand for antibody testing and serology that’s going to be – it’s really going to make the demand for PCR testing look minimal, I think.
And so, we have to get that if that’s going to be part of the national plan at all, it needs to come a long way before it can really be in a position where it’s ready to be utilized in any sort of testing plan for reopening the economy.
Q: Great. And since the other reporters got to follow up, what’s the significance of the positivity rates of the PCR testing and what should we be looking for? What are you looking for in that trend over time?
MICHAEL MINA: Well, certainly we’re looking for – the nice thing about PCR versus antibodies, and we can get some similar data from antibodies, but it tells us what’s going on now. And so, we want to see that going down, and that will at least tell us that the curve, that at least for this particular wave of the epidemic, that we are bringing it down. And I think that seeing the positive rate of PCR tests drop week after week is an encouraging sign that, or will be an encouraging sign, that this virus is essentially listening to us and playing well with us when we said that we were going to social distance.
And I think by all metrics, it is. Seeing the curves turnover at a national level, it’s certainly a much larger, sort of wider distribution and bump. But in sort of more geographically-centered places, we can see the effects of social distancing take place in terms of both reduced cases that are showing up in the hospital. If we look only at the numbers of positive rates, it really does obscure things because as testing has become more widely available, we’re testing more and more people. And that’s just leading to an absolute number which is potentially still going up, so it doesn’t exactly tell the whole story. If we see the number of continuing going up, we have to recognize that testing continues to also become increasingly available over time to a certain extent, and in particular, more widely available outside of the hospitals. And so, we have to be cognizant of what the data is representing. It has shifted dramatically over the course of this epidemic in terms of who’s getting tested and what it means.
MODERATOR: Okay, next question.
Q: So, Mike, when you when you say that you demand for a serial article testing to dwarf the current demand for PCR testing, can you paint that picture, a bit of what you’d like to see happen both in the near term and the longer term? What’s already being done and what’s actually doable in terms of using serological testing? Thank you.
MICHAEL MINA: Yeah. So, what’s happening now is we see kind of the – I feel like it’s Groundhog Day all the time now, or maybe this is more like a déjà vu, I guess. The echo of what happened with PCR, as we see Roche, and Abbott, and DiaSorin, and some of these really large companies beginning to develop their serological test, clamoring to get FDA approval and saying that they’re going to have millions of tests available soon.
You know, we’ve heard that before. And these companies often make pretty large proclamations about how many tests they might be able to do and what the throughput is. Those are all sort of theoretical throughput, some theoretical amounts that they’ll be able to make. Including, in particular, the instruments themselves are busy doing other things. So, these instruments, they might say they can run 4,000 tests or something, but when it comes down to it, actually, most of these instruments are in use for lots of other assays in the hospital. So, you’re going to see these companies start really getting these tests approved and starting to get reagents in the hands of clients, but those clients are largely, initially for those types of commercial tests, they’re going to be hospitals. These are not going to be useful for the average person who’s out of the hospital. And hospitals don’t generally, you know, provide services for surveillance public health-type efforts, which are really what we’re going to need here.
So, in that sense, I think we’re pretty far away from having sort of any sort of production capacity for the type of surveillance we will require. It was very different for PCR because most people, it was at least something you could say to people in the community, you could say, you know, you’re only getting tested for a virus if you’re sick. And that makes sense because, you know, that’s what we normally do for viral infections. But for antibodies, everybody us going to want a test, I suspect. I think everyone’s going to want to know their status. We don’t even know how to interpret them yet, which is another issue.
But I think we have to really think hard about what is going to be – how are we going to make this available to the average person, and maybe it will come down to the sort of pregnancy test model that are just little plastic throwaway thing that shows a couple of lines if you have IGG or IGM. Those have been routinely difficult to build and build reliably, but I can’t imagine that there is not a huge number of companies that are working to improve upon the sensitivity and specificity of those and to get them out into the hands of consumers as readily as possible.
We do have some efforts ongoing here in Boston where we are, instead of going with Roche and Abbott for a population health perspective, we’re building our own ELIZAs and this is with a few different institutions between Harvard and MIT. We’re sort of all collaborating and bringing together resources to build very highly sensitive and highly specific tests and get them built onto robots in a way that was very similar to what we did at the Broad Institute previously to get a high throughput PCR testing available.
There’s going to be efforts across academic institutions, I think, to stand these types of tests up on robotics and automation and just start doing this as part of these large serological surveillance studies. And certainly, we’re planning to do that and I know that many other places around the country are doing that. But even with these major academic centers really trying to get high throughput testing available, I think it’s still not going to be sufficient. And that’s because we might have people wanting to be repeat tested, you know, many times. Maybe we’ll have you know hundred million people who want to be tested every couple of months. And that’s actually quite a lot of tests to build.
MODERATOR: Okay, next question.
Q: Hi, thanks for taking my question. So, I have two parts to this question. It’s a bit of a follow up to what you were just talking about. And the first question is, you know, obviously we’ve seen I think at this point four tests that have been approved, serological tests that have been approved by the FDA. There’re already some questions about the reliability of one of those tests. And so, I’m wondering about two aspects of this, you know, following up on what you were just talking about, the need for a huge volume of testing.
And one is how confident are you about the reliability of the tests that have been developed and about how soon we’ll be able to know that we have some, you know, variety of highly reliable tests that can operate on different platforms? And then the second part of that is given how with PCR tests, we’ve had huge bottlenecks because of access to supplies needed for those tests, is there any reason to believe that that same problem is or is not going to occur when we talk about serological tests?
MICHAEL MINA: Yeah, so, certainly the second question is – I think that there’s going to be an enormous backlog of reagents for these tests and that’s part of the reason why I think, going there, Roche, and Abbott, and all these companies, I think they will likely have a backlog. These tests aren’t as complicated to produce and develop as the PCR tests. So, hopefully, you know, there will be extra supply, but I am fully expecting that the hospitals will again be put on allocation, and these tests will kind of be given to one hospital this week and another hospital that week, and there won’t be plentiful tests available. There might even be gaps where there’s no tests available. And so, hospitals will have to do essentially what we’re doing with the PCR tests, which is really ration them decide which ones we’re going to run in house with the quickest tests, which ones we can send out, whether it’s to the Broad for pretty rapid turnaround, or maybe to Quest lab sort of thing. And, you know, so you have to kind of make these bins and triage them appropriately.
I think the exact same thing is going to happen here. You know, maybe there will be priority for example for healthcare workers and we’ll really have to figure out how to work with the industry partners. And again, I think one of the major things that we learned in the first phase of this with PCR is redundancy. We absolutely need to ensure that we have redundancy, because on any given day, you might not get your shipment of reagents from the company and you have to quickly pivot and turn on a different machine than you’ve been using.
And I think that will help us get through it. But again, I don’t think that we will see the type of supply that will come close to really meeting the national demand. It can potentially meet the demand within hospitals for their patients, but I think in this case, the vast majority of demand will come from the outpatient setting or just the average person sitting at home, for example.
Q: Okay, and then with regard to the reliability question?
MICHAEL MINA: Yeah, so that’s been a really big question and I think it does come in – there’s a couple of parts to that. One is reliability in terms of the actual value you’re getting. And if it’s wrong, if it’s saying that you’re positive and you’ve actually never been positive, and negative and you’ve actually been positive and so that’s sort of just inaccurate results.
And then there’s a different question, which is are there going to be accurate results that can be quantitative, or somehow give you some reliable indication of immunity. And the indication of immunity – well, I’ll answer both. So, I think the reliability, we saw pretty poor results coming from some of these point of care instruments that were initially rolled out and sort of flooded the US market and the European markets and everywhere else. And those have proven to be not particularly reliable and people are actually regretting their decisions to purchase these. And it’s important if you’re using these for public health, just one – you know, if you have something that is just 2% non-specific or 98% specific, that actually becomes a big problem. You really want something that’s over 99% specific for a lot of these efforts.
The other question though is really on what is – will we have results that are sufficiently accurate and quantitative to be able to tell somebody that they’re actually immune? And that’s a whole different question. Most of these tests actually won’t be giving you a quantitative value, which is going to become a problem if the correlates of immunity, or if we’re looking at results that can provide correlates of protection.
We still don’t know what those are. And I think the point is we, there’s a lot of people who are wanting to use immunological or serological testing to get their employees back to work. And that’s for obvious reasons. But there’s an underlying assumption there that people who have antibodies and have been exposed to this virus will have some level of immunity that not only protects themselves from becoming infected and symptomatic, but also protects them from being transmitters onward of the virus and, in particular, it’s that second piece that bothers me the most. I don’t think we have nearly the immunological and biological data at this point yet to be able to say that just because somebody has a strong enough immune response that they themselves are protected from symptoms.
I don’t think we can necessarily say without real in-depth investigations, which are ongoing, that they cannot be transmitters and potentially transmit to somebody else. And so those are – we’re developing those studies now to try to understand what might be the correlates of protection and what do those correlates mean, I think it’s going to be at least a few months before we have a lot of that information.
MODERATOR: Thank you. Next question.
Q: Hi. Thanks very much. We’ve had a number of recent reports in recent days – an aircraft carrier with a bunch of sailors, a homeless shelter in Boston – where there have been a lot of asymptomatic cases supposedly reported. What did these new pieces of information – also from Iceland, where they did a nationwide sampling screening. What did these pieces of information add to our understanding of that situation – the asymptomatic and true infection rate? And what implications might that have for getting people back to somewhat of a new normal?
MICHAEL MINA: Yeah. Well, I think I will put my cards on the table and I have a bias from my experience helping so much with the testing of this virus. I feel fairly strongly that we have just been off the mark by huge, huge numbers in terms of what’s the true cumulative incidence of this virus in the population. And it’s a very hard thing to know because testing for virus was just getting going more or less everywhere in the world as this virus was starting to spread, so there wasn’t a really good way to know how many people are we missing through viral testing. And of course, there was the New England Journal paper that came out two days ago that showed something on the order of 15% of pregnant women in New York City were actually positive for virus upon admission into the hospital.
And that, to me, tells me that is an enormous number for being virus positive, that means there’s an even larger number that was that would have been antibody positive if they were measured. Because, again, the virus is just a transient window in time into somebody whereas antibodies are a little bit more lasting and so, I think we’re starting to see an increasing number of studies that are pointing to larger portions of the population that have been exposed to this virus and don’t have symptoms
And this isn’t surprising to me at all if we continue to see this, because I think we have done such a poor job with testing for a virus that my personal belief is that almost all of the data we have collected so far, nearly everywhere in the world has been confounded by changes in testing practices and things that are very difficult to disentangle. And we may be have fooled ourselves into thinking that we’re capturing more of the cases than we are. Now how often we have been, you know, it’s hard to say. But to see these community centers, or the homeless shelter that you referred to, and other groups where there’s a lot of positive results in particular, serologically, but very few symptomatics, I think that it starts to paint a picture where maybe this virus, especially in younger individuals, you know, those who are not at excessive risk, so maybe people under 60 years old, for example, maybe actually the asymptomatic cases are much more common. And we’ll start to detect those, the more we do antibody testing in a sort of unbiased approach, or even just coupling different types of biases.
But as long as you’re aware of what those biases might be as you’re testing people, I think we’ll start to learn more and more about just how widely distributed this virus has been. And that number, whether it turns out that we’ve had like 1% of the population infected, or 10 or 15% of the population infected, is going to really be crucial to sort of the decisions we make next as a population, because it will tell us about the biology of the virus, how virulent and pathogenic is it really. And it will tell us about how transmissible it is, which will impact on how we open up sectors and it will tell us how much herd immunity there may or may not be.
The worst-case scenario is that the current, sort of, most common thinking where we have maybe a few million cases in the world, that would be a devastating result to come to find that we’ve actually captured most of the of the positive people through the PCR testing because that would mean that this really is a virus with 1% or 2% mortality rate. But I think that in general, we could potentially find that we are 10 times or more off the mark in terms of how many cases there really have been and, you know, that would be a good thing. It would mean that many more people have gotten this and didn’t have to go to a doctor, and so I think that there would be a lot of benefit and it would be a good sign if we actually see that but the studies are just starting. We are seeing hints of it. And I think that that study in New York – there was a study in the Netherlands that just came out that showed 3% of blood donors were positive in the Netherlands, but that was actually, those samples – the way that that study was set up means that those people who were positive probably were infected back before about March 25. So that could suggest actually that maybe 10% of the Netherlands would be positive if you went and did another point prevalence today or cumulative incidents with antibodies today.
So, we don’t know that and I’m just sort of doing the back of the envelope calculation there, but I do think that we might have a very different view of things in this whole virus within the next few weeks as some of these serological studies continue to roll out.
Q: Follow up, you just mentioned something about what we need to do this in an unbiased approach. What do you mean, as opposed to like specific samples? What does it mean to find it, like at a homeless shelter or in one city? Can you expand on that?
MICHAEL MINA: So, there are certain areas where we anticipate that if transmission happens that we will that it would infect many people and so, extrapolating too much from sort of Diamond Princess or nursing homes or homeless shelters, that can be dangerous, because that might not represent, you know, the suburbs and the vast majority of people in the United States who don’t maybe live in in really deep metropolitan areas. At the same time though, those types of studies, even focusing in on those sort of hotspot places, what they can do, they might not tell us the whole story about transmission across the whole population, but what they can do is they can tell us a lot about what’s feasible for this virus to do, what does it have the potential to do. And I think that we’re seeing such widespread transmission and in various – in community centers or homeless shelters or nursing homes or, you know, ships. I think that tells us that biologically, this virus is able to move extraordinarily quickly through populations.
But to really feel good about giving, you know, the White House or whoever a document that says, you know, this is what we think is the prevalence of the population, we don’t have to test everyone in the country to do that. We can be smart about it and we can design studies that look at different groups of people with different socioeconomic backgrounds, different geographic backgrounds, race, ethnicity, gender, and we want to make sure that we capture all of these different features that ultimately give us what we call a representative sample of the population.
And that’s sort of what we need to be looking at to really make very good claims. But, and it is tempting, and I certainly do it quite a bit, I look at what data is available and start to make projections and based on biased studies because those are the ones that we technically have, but I think we can actually learn a lot from those because we do see that there is just an enormous number of hotspots actually for this virus. So, it’s not, sort of, a one-off thing. We’ve seen that this virus is really capable of transmitting and in sort of any place that has any remote chance of being a good place for transmission, it does. And so, I think that it’s proving to be a very formidable opponent in that sense, in terms of its real transmissibility. But ultimately the unbiased samplings of the population will really help out a lot.
MODERATOR: Next question.
Q: Hey, thanks so much for taking my question. And this goes back to something you said earlier. It begs the question, to a certain extent we keep talking about we will have a second wave at some point. But if – you were saying you don’t even know that we’ll have adequate testing four or five months out. When might that second wave hit and when would we even know it, because we might not have the testing regime in place necessary? Thanks.
MICHAEL MINA: I mean, that’s one of the most important things here. So, I think that, in general, we’re doing a very good job, relatively speaking, of social distancing. I think it’s been pretty remarkable to see all populations social distance sufficiently, to actually get this virus to start plateauing and hopefully turning over. And we’ll see the fruits of our labor soon in the hospital-level data. And I think we’re already seeing it in terms of just overall sickness. But that essentially means that we have a lower number of people who have been exposed than we otherwise would have, which is a good thing. That was the absolute objective, but it means that we are certainly at risk for another wave of this.
And we don’t know when it might hit. We will probably continue social distancing across the country, at least for – you know, I think I can speak for where I live here – I think that we should be continuing to social distance for another four or five weeks until we see the sort of decline continue on and on, down and down, and probably into June. But then the question is, once we open up, we don’t really know exactly what’s going to happen. We have no idea really whether this is going to bounce back the moment people start going back outdoors or if summer is actually going to, or the warmer weather is actually going to help us out.
I think that we can anticipate, though, that if it doesn’t happen in the summer, we’d all be very surprised, I think, if we don’t see some reemergence in the fall. And the good thing is that hopefully the social distancing will be enough to get the virus to sort of get to low enough level so that when we open back up, we can do a very good job at surveillance, and people can be acutely aware of when they might have symptoms and sort of hopefully not go into work and do their best to stay home.
But I do think that once we open things back up, it’s going to be hard. I think we really will run the risk of a new wave of this infection. Either it’s going to happen in June and July, if it turns out that it’s just the force of infection is just so great because the number of susceptibles is so great. Or it will happen as the fall comes back in. I don’t anticipate the virus is going away. So, we can’t say exactly what that’s going to look like and I think that as we start opening, we’re going to be very smart about how we open up different sectors of the economy. And I think that it does need to be a phased-out plan. And I think that’s important. We can’t just say everyone you know go back to work tomorrow – it needs to be done methodically, it needs to be done with greater surveillance than I think was put in place with the report.
And I think that it’s going to be an intense experience to start to see how people go back to work initially, and what type of testing people might have. I think there’s going to be a lot of fear, that people are going to be fearful, that they might be sick or their loved ones might be sick when they go back to work, and it’s unclear what all of that’s going to look like.
MODERATOR: Alright. Next question.
Q: Hi, Mike. Thanks for doing this. I wondered, do we know of any cases that have been transmitted from surfaces and is there actually any way to figure that out?
MICHAEL MINA: It’s a really great question. You know, I don’t know the answer to it. In terms of the hard data that might have shown definitively that there would be a transmission from a surface and that it couldn’t have infected somebody in any other way. I absolutely think it’s likely that it happens. And in fact, I think that it’s probably quite common, if not as common as droplets, you know, almost as common. When we look at the Diamond Princess and see just how many people got infected, it’s very unlikely, I think, that that much of that transmission may have happened through contact rather than droplets.
But I don’t know if there’s been a good study to really definitively sort of rule it in as the definitive mode for an individual.
Q: Thank you.
MODERATOR: And last question for today.
Q: Hi, Michael. How are you?
MICHAEL MINA: I’m doing great, thanks.
Q: What’s the percentage we need for herd immunity? Is it plus 50%? Because R0, by definition goes below one.
MICHAEL MINA: That’s absolutely correct. So, herd immunity, I would say that there’s two sort of thoughts with herd immunity. In the same way that we can have incomplete personal immunity, someone might have immunity but still be able to get mildly sick, we can have incomplete or partial herd immunity, which is essentially that you can still have some transmission throughout the population, but it’s not as great as it would be. And that’s essentially what we go for, for example, when we try to vaccinate people for flu every year. We understand that the vaccine isn’t 100% protective for everyone, but we know that by vaccinating at least a fraction of the population, that we will abrogate flu epidemics per year.
So, on the one hand, any bit of immunity in the population adds to some level of herd immunity. But the real question is what’s the level of immunity in the population that is required to prevent onward transmission from occurring overall and to get R0 were they effective, we call it, or below one. And that is – there’s a simple equation and it’s one minus one over R0. And so, if this turns out to be an infection, a virus with an R0 as on average three, then we would anticipate that we need about 66% of the population or so to be adequately immune. And if we believe that maybe the R0’s higher and that there’s actually quite a large number of people who have been infected asymptomatically, for example, then to really prevent onward transmission, we might need 85% of the population. This is why measles, with an R0 of 18, you have to vaccinate and get 95% of the population immune. So, it scales linearly in that fashion.
Q: Okay, and just real quick, another one. What are the odds that it’s very transmissible simply because nobody had immunity and therefore, you know, that’s kind of an illusion?
MICHAEL MINA: I certainly think as this epidemic grows and continues marching forward, I think that we might find that this virus looks more and more – not that it’s not a bad virus. It’s clearly very lethal for vulnerable populations, but I think that one of the most extra ordinary aspects of this virus will not be so much the virus itself, but the extra ordinary number of susceptibles, which was essentially 100% of the human population.
And so, I think that that can’t be ruled out. And I do think it plays a huge part in the devastation that we’ve seen to the health care system. My feeling is that we will find that this has infected many more people than we think and that the healthcare system is in such disarray because of the sheer absolute number of infections, maybe at least as much as it is because of the true virulence of the pathogen. And the transmissibility is certainly linked into the number of susceptibles.
We know that it’s going to burn through whole populations, even if it was not the most transmissible virus in the world. When you put it into a population that’s 100% susceptible, you’re going to see sort of that theoretical R0 play out, whereas most viruses we deal with, we have a good deal of population immunity, at least cross-reactive immunity built up.
This concludes the April 17 press conference.
Karestan Koenen, professor of psychiatric epidemiology (April 16, 2020)