Coronavirus (COVID-19): Press Conference with Stephen Kissler, 3/23/22

You’re listening to a press conference from the Harvard T.H. Chan School of Public Health with Stephen Kissler, research fellow in the Department of Immunology and Infectious Diseases. This call was recorded at 12:30 p.m. Eastern Time on Wednesday, March 23rd.


MODERATOR: Dr. Kissler, do you have any opening remarks?

STEPHEN KISSLER: Yeah, just looking forward to speaking with you. I’ve mentioned in the intro that I’m happy to talk about the BA.2 wave. I recognize that it’s not really a wave at this point yet in the U.S., but hopefully we can dig into a little bit more… What things might look like while recognizing that there’s still a ton of uncertainty.

MODERATOR: Great. Thank you. And it’s been a while, so might be a little rusty with this, but we’ll get right back in the saddle. All right. Looks like we have a couple of questions already. First question.

Q: Hi, thank you so much. Just wanted to… and this was not specifically on your list of things that you said you could talk about today. So sorry if it’s too off subject. Let me know if it is, but I just was wondering if you had any reaction to the news that Moderna is seeking authorization for children under the age of six and what you thought of that and any thoughts you could share?

STEPHEN KISSLER: As always, I’m most excited to just see what the data look like, and I know that there’s more data that’s been collected that I haven’t yet seen. But, I think it’s very promising. I know that one of the things that especially parents of young kids have really been waiting for is exactly this authorization for the youngest age groups. I do think that, assuming that the safety and efficacy holds up well in that age group and is durable over time, that it would be great to have these vaccines available for young kids. I think as I have mentioned before in previous calls, but I think it bears mentioning again now, that it’s also to bear in mind the difference between approvals and recommendations. Again, as long as the safety and efficacy do continue to hold up, I’m a very strong advocate for approving vaccines for the youngest age groups. There’s a much broader conversation than that needs to be had about recommendations for kids in those youngest age groups, just given that their risk profile from COVID-19 just differs so much from older adults. But, especially having those vaccines available for kids who have immune conditions that might not allow them to mount a good immune response to COVID-19, I think the vaccines could help in some of those cases who have other sorts of respiratory conditions. I think there are a lot of kids who could really benefit from these vaccines, not to mention their families as well. So, I see it as a great step in a good direction, and I’m excited to see more.

Q: Just to have a good quick follow up on that, is, I mean, it says it’s 43.7 percent efficacy in children six months to two years old and and then just 37.5 in two to six. Is that disappointing or surprising in any way that the numbers are not higher? I mean, in adults, it was a much higher levels of efficacy.

STEPHEN KISSLER: It’s difficult to compare the statistics on efficacy perfectly from one point in an epidemic to another, but it’s not surprising to me that there would be differences here for a couple of reasons. One is that the immune systems in young kids differ hugely from the immune systems in older adults. But, in my mind, probably the biggest thing is that the size of the dose differs quite a bit too. With smaller doses in young kids, you might expect a smaller immune response as well. So, I’m not surprised. But that said, the efficacy, while it doesn’t sound great, is actually roughly in line with the efficacy that we sometimes see from the seasonal flu vaccine and that also can be very helpful for young kids to keep them from getting really sick from the flu. So, I think that there is precedent for using vaccines of about this efficacy in young kids. And while, of coursem I would love to see a 100 percent efficacy on all of the vaccines that we have available, I do still think it’s high enough to be pretty useful.

Q: Thank you so much.

MODERATOR: Next question.

Q: Hi, thank you so much for taking my question. I do have a few, and that’s also piggybacking off of the Moderna question that was just asked. This phase three trial was done during the recent Omicron wave. Do you think that this vaccine could protect young children against BA.2, too? Is there any reason to believe that it wouldn’t?

STEPHEN KISSLER: In my mind no. It seems like BA.2 and previous sub variants of Omicron BA.1 and its sublineages, have… They interact with the human immune system in pretty similar ways. And so people who have been previously vaccinated or previously infected seem to fare pretty similarly when exposed to BA.2 or BA.1s. My expectation is that, even though the vaccine trials were done for the major Omnicron wave in the U.S., that we should see pretty similar results for BA.2.

Q: Great, thank you. When do you think that we would see the vaccines available for young children and elementary school children and when would we see a surge of BA.2? I guess the question would be… Will children get access to these vaccines before the surge happens?

STEPHEN KISSLER: At this point, the vaccines could be made available to those younger age groups in pretty short order. This is pretty different than the initial rollout of the vaccine, simply because it is essentially the same vaccine, just in different doses. The vaccine is available, it’s been produced in high quantities. It’s fairly widely distributed right now. So I think, pending approval, it’s difficult to say how long that might take. But I think that that could be pushed forward pretty quickly, ideally within the next couple of weeks, probably especially if we’re expecting a surge from BA.2. I think that we could see approval for young kids to get the Moderna vaccine pretty soon. The question of if and when a surge is coming and how large is also very much open. I know that we’ve seen major surges that are dominated by BA.2 across much of Europe. But, in contrast, for example, in South Africa, we saw a major BA.1 wave, that’s where they saw the Omicron wave first. And now, there’s a lot of circulation of BA.2., but it hasn’t really caused an increase in cases so much as it sort of lengthened the decline and given that epidemic a very long tail. It’s not totally clear what’s going to happen in the U.S. In many ways, our experience with Omicron. There are some similarities between both Europe and South Africa, in terms of our vaccination rates are maybe a little bit closer to those in Europe, but we also did see a very intense BA.1 wave. And, to the extent that gives us protection against BA.2, we might see dynamics somewhat more similar to what’s happening in South Africa as well. So all of that is to say that, I do think that it’s possible to get approval of the vaccines for these youngest age groups soon and probably soon enough to deal with whatever BA.2 is going to throw at us in the coming weeks. But that said, I’m still not totally convinced that we’re going to see a major surge from BA.2. And we’ll just have to see on that.

Q: Great, thank you.

MODERATOR: Next question.

Q: Hey, there. Thank you. So I have a question that’s maybe a bit further out than just whatever might be happening with BA.2. So, into the future, there’s going to be these waves and maybe there’ll be seasonal and how damaging they are will kind of be influenced by things like viral evolution and potential waning. But, I guess one thing that struck me so far is that even between waves, we’ve never actually gotten down to really low levels like below 10000 cases a day or something like that. And so I’m just wondering… What do you think might the quiet periods look like going forward? Is it just that we need a bit more experience with the virus before we can get to low levels or is it possible that there’s just a persistent plateau outside the waves that just slowly ticks along and causes some amount of morbidity and mortality?

STEPHEN KISSLER: I really appreciate this question a lot. It’s hard to say because this virus is in many ways different from just about anything that we’ve seen previously. So I can give a couple of examples. So one, of course, is flu where we have seasonal outbreaks, but then it reduces to very low levels in much of the U.S. during the summertime and that’s reflected across most temperate regions of the globe. One possible future that I could envision is that with repeated exposure to SARS-CoV-2 will essentially reach a similar equilibrium point where we have large outbreaks, potentially in the winter season or in times when people crowd indoors and substantially lower cases in the summer. Basically, just once it reaches that cycle where it’s depleting, it’s basically infecting a lot of partially susceptible people during the winter, but then that provides enough immunity to sort of get us through the summer. But one reason why that might not be the case is because SARS-CoV-2 is just so incredibly infectious, especially with the rise of Omicron. And so because of that, it may well differ from the dynamics of flu where we do see persistent spread over the summer. The other example that I always think about when it comes to highly infectious respiratory viruses is measles. And with measles, we also tend to see really significant outbreaks. At least in the pre-vaccination era, we saw some major outbreaks in the wintertime, and they tended to sort of subside as well outside of the winter. But that’s also different because measles gives you a much longer lasting immunity, it seems, than infection with SARS-CoV-2 does. So generally, young kids would get measles, but then they’d be pretty much protected from reinfection for the rest of their life. SARS-CoV-2 is different because we can continue to get reinfected by it. So, in my mind, the most likely scenario is that we’re going to settle into a seasonal pattern of SARS-CoV-2 spread where it’s going to dominate probably in winter months, in temperate regions of the globe. But that, actually we’re not going to get quite down to those low levels of spread over the summer and that there will be a lot of variation, but it won’t be quite like flu, where there’s almost none of it. But we’re going to kind of be dealing with this at some level at all times in the year.

Q: That’s great, thank you very much.


MODERATOR: Next question.

Q: I just wanted to get some idea, given all the unknowns. What would you expect, if there is a surge, for this to look like among the various populations in the United States? The vaccinated pop., the fully vaccinated population, the partially vaccinated, the unvaccinated, the elderly versus the young?

STEPHEN KISSLER: Yeah, thanks. So in many ways, I think that it will likely resemble our experience with COVID 19 up until this point. One of the key things with Omicron, and this goes for BA.2 as well as all other sublineages of Omicron. Is that a booster dose, a third dose of an mRNA vaccine or an mRNA vaccine on top of a Johnson and Johnson, if that’s what you received before, really goes a long way towards helping protect you from symptomatic disease and especially from severe disease. Probably the biggest delineation that I imagine seeing is that people who are boosted will probably fare better than people who are unboosted. And I think that’s probably the biggest split point. We’re going to continue to see, I imagine, the standard increase in severity and the likelihood of hospitalization, for example, and even the mortality rate that goes up substantially with older age groups. But, it still seems to be the case that, even now, a few months after a lot of especially the older age groups have gotten their boosters, that a vaccinated and boosted person over the age of 75, their risk is probably on the lower, if not lower than a unvaccinated 20 year old. And so that’s good and in many cases, might be even better. So, I think that the most important thing is that even though, if you control for everything, the risk still increases substantially with age, that with vaccination and boosting even the oldest members of our society are are pretty well protected. And it brings the risk from COVID 19 back in line with a lot of other risks that we tend to face or faced from pre-COVID time with other infectious diseases. Hope that helps a little bit. There’s so many different subgroups and populations to think about here. People are returning to work. I think that the question of… Gosh, I think it’s beyond the scope of this call for me to be able to break down all of the issues — the breakdown by racial and ethnic groups, the breakdown by socioeconomic groups and specific subgroups of people who may be immunocompromised for COVID-19 still poses a big risk, young kids who still have not been vaccinated. I think there are a lot of really important things to distinguish there. But, if I don’t go into all of the details with those, it’s not that they don’t matter. But that I think some of the biggest differences that we’re going to see is between boosted and unboosted and then continuing to see this gradient by age.

Q: Sorry, I re-muted myself, I’m all set. Thank you very much.


MODERATOR: Next question.

Q: Hi, thanks for doing this. So you mentioned when talking about the BA.2 potential wave about how there is a lot of uncertainty. And I’m wondering if you could walk us through the factors that lead into that and the different variables that you’re considering when trying to look ahead and figure out how severe a potential wave might be.

STEPHEN KISSLER: Yeah, thanks. The variables I usually look at when making these forward looking projections is first the immunity in the population as a whole. I am a modeler. I use models to try to understand what might happen next. But oftentimes the best thing that we can do is compare what’s happening now with what has already happened in other places that are similar to us. That reflects some of the things that I was mentioning earlier about the experience in Europe versus the experience in South Africa. So, when looking at what’s happening in the U.S., one of the things that I bear in mind when trying to compare our experience with other countries is that we have decent vaccination rates, although certainly lower than many of the more highly vaccinated countries and in Europe, especially. But, we have also had a lot of previous transmission of Delta, of Omicron, and of even SARS-CoV-2 prior to those variants. So, all of that is contributing to, actually, quite a bit of population immunity. And so, the more immunity we have in a population, and especially the more immunity we have to variants that are related to the thing that’s currently circulating, the less chance that I see of a major surge. The second major thing is really just where we are in the year. So, seasonality is certainly just a factor among many that’s driving the spread of SARS-CoV-2. But, I think that one of the things that might help us as we’re going into this next surge is that we’re entering the spring, which seems to be sort of a low time of circulation for SARS-CoV-2 across the U.S. In some parts of the U.S., we’ve seen major surges in the summer, especially the late summer. And then, in others, we’ve seen it more in the winter. But, usually spring is the time when we’ve seen lower cases across the U.S. And so, whereas we’ve seen BA.2 surges in much of Europe during times of year when you might be expecting to see a surge anyway, the increasing prevalence of BA.2 in the U.S. is more coming along a time when we might expect to see cases declining anyway. So, to summarize that, I usually look at seasonality, I look at how much immunity we have for the baseline and to things that are related to the things that’s circulating now. And then, the last thing to measure is to project severity overall in the population, number of deaths, number of hospitalizations. Really, the most important thing is the vaccination rate in the very oldest age groups because those are the people who still tend to be at highest risk of going to the hospital. So the higher our vaccination rates are in that age group, the better chance that we have of not having major surges in our hospitals.

Q: Great, thank you.


MODERATOR: Next question.

Q: Thanks for doing this, so kind of piggybacking off of that last question. I’ve been talking to some folks right now. Obviously, Europe’s getting hit hard by BA.2 right now. But, every country is having their own experience. And given that experience in Europe, what are you thinking as far as regional differences with how BA.2 hits the US? And which parts of the country are you more concerned about? I’m guessing it’s those that may not have as much immunity, either from from vaccines or from exposure that you can walk us through which states or regions you’re most concerned about.

STEPHEN KISSLER: Yeah. So actually, in my mind… In many ways I’m concerned just about everywhere equally, but it’s the timing of my concern that really changes. So, here in the Northeast, it’s already the case that, at least among the viruses that we’re sequencing, which is… we’re sequencing quite a bit here now… Most of them, so over 50 percent, are BA.2. And so, it’s often the case that once the variant passes that 50 percent mark, we really start to see what it’s going to do. So, if it’s a more transmissible variant, we start to see an uptick in cases, for example. And so, in many ways, I think that it’s going to be the coasts and especially the Northeast that are going to see what’s going to happen from BA.2 first. But, as has happened with most of the previous variants as well, really nowhere has been spared. It’s really just been a matter of timing. And so, I think that when it comes to trying to measure the relative severity of different places, a lot of the same things are still going to hold. So, certainly if there’s lower previous immunity, a place might fare worse. If there’s much higher population density or a higher concentration of older individuals, they may well fare worse. But, none of this really differs from previous waves of SARS-CoV-2, and I think the biggest difference that we’re going to see between places is maybe not so much the severity, but just the timing.

Q: Thank you.

MODERATOR: Next question.

Q: Yeah, hi, thanks for doing this and taking my question. I’m wondering if you can talk a little bit about the role of mathematical modeling in making predictions about the pandemic. Is it something that is most helpful in terms of identifying patterns that could lead to surges in the future or identifying anomalies that could indicate the emergence of a new variant?

STEPHEN KISSLER: Yeah, thanks. I think there are a number of different ways that mathematical models have been used well and plenty of ways that we’ve not used them as well as we would have liked as well during the pandemic. But, I think that at their best, there are really two main areas where models can be helpful. The first is in making short term forecasts, so thinking about models as the equivalent of weather forecasting tools, for example, where we’re trying to make a prediction over the next couple of weeks. What’s going to happen in a specific community? And that can be really useful, especially for planning very short term responses. So, I think that those kinds of things are very helpful for local policymakers, for hospital administrators, for people who are trying to prepare capacity to do contact tracing, to deal with an influx of patients. And so that’s one area where models can be very useful. But, of course, those forecasting model, as with weather forecasts… Weather forecast for Connecticut is not going to be particularly useful for me sitting here in Massachusetts, and we’re actually not that far away anyway. So, with those kinds of forecasts, they need to be very precisely tailored to the populations that they’re dealing with. And that makes them a lot harder to sort of use broadly. So, that brings in the second area where models can be really useful, which is as these contingency modeling frameworks. So they’re these mechanisms for asking complex, “if then” statements. So, you can say, “if we vaccinate 10 more percent of our population, roughly, how much do we expect the number of hospitalizations to decline in the next wave?” So, you can use mathematical models to sort of get these rough orders of magnitude estimates of how a certain policy change might affect the spread of an epidemic across an entire country, for example. And then, that allows us to compare different choices. We oftentimes have different choices of what sorts of policies we might be able to enact, and we want to make sure that we’re using the ones that are going to be maximally effective while being minimally intrusive or minimally costly. And so, mathematical models can be really good at that for just trying to get a rough sense of which policies are the optimal ones in those kinds of scenarios. They won’t give you as precise estimates because, again, we’re dealing with the entire epidemiological scenario in a location as a whole. It’s sorta like the analog of climate modeling as opposed to weather modeling. It’s trying to understand what are the broad trends in the epidemiological climate over long periods of time. So models can be useful in both of those areas. I think it’s really important not to confuse the two types of modeling because usually one doesn’t behave well for the other purpose and vice versa. But those are the two areas where they’ve contributed most during this pandemic.

MODERATOR: Are you all set?

Q: All set. Thank you very much.


MODERATOR: Next question.

Q: Hi, I was wondering if you could expand just a little bit on the scenario you described of a permanent COVID season as opposed to flu seasons in the fall. Like what that might look like as a public health departments on the county level or regional saying like, “look out, we have COVID” or how do you see that playing out? And also how much confidence do you have in that versus another surprising variant like Omnicron, which we’ve been told is genetically quite distinct from the other ones and sort of screwed up our expectations somewhat occurring now? How much, on the other hand, should I throw into the story?

STEPHEN KISSLER: Everything in the kitchen sink, I guess. This virus has managed to find a way to surprise us at every turn. And so, I think with everything that I’m about to say it, that’s worth bearing in mind, that there could be some new variant that emerges that’s quite distantly related from anything that we’ve seen recently. That really could change a lot of this. And so, that said, my sense is that with this… Gosh, that’s really such a disheartening term, but the sort of a permanent COVID season. I do think that we’re going to see substantial ebbs and flows in different places at different times. One of the things that I didn’t really get to talk about as much in some of the previous questions, but I think that does apply to them and to this, is that we’ve been talking about seasonality and really seeing rises in cases during the winter months. But in a lot of places, especially in the Southeastern United States, I think Florida, for example in particular, we’ve actually seen a lot of spread during the summer. And, I think that some of that could be down to just the time when people spend indoors. And so, I wouldn’t be surprised if we end up in a scenario where we actually have some kind of opposite seasonality between different parts of the country based on whether you’re retreating indoors for air conditioning or for heat. Because it really does seem like unmasked indoor interactions are far and away the highest risk exposures for spreading SARS-CoV-2. So, we may settle into a seasonal pattern that looks different in different parts of the country. And then, we’re also going to have some of the sporadic variation that just depends on introductions and differences in immunity and differences in age groups that will change the timing of cases from place to place. So, actually, what you suggested is kind of what I envision is that over time, we may have sort of a COVID weather report that is just roughly tracking cases locally. I think that’s going to be probably largely based on things like passive surveillance. So, the number of people who are seeking outpatient care for respiratory viruses that turn out to be COVID. A lot of wastewater surveillance, for example, because I think that the number of people who are proactively going out to get tests is going to continue to decline for a while. And then, the last thing I think that’s worth mentioning here is that… In a lot of these discussions, we think a lot about policy changes and whether there’s going to be the political and individual will to change our behavior if cases do start to rise. And, on that score, I’m actually a little bit more optimistic than some of the people I’ve spoken with lately. In that, for much of the pandemic, we’ve had policies that have certainly changed the ways that people interact. But, it seems from a lot of the evidence that I’ve seen, that oftentimes people also spontaneously change their behavior based on how much COVID is circulating in their community. Our tolerance for COVID cases is probably going to increase as people are increasingly immune to the virus, certainly. But, I think that in many ways, one of the best things that we can do to help manage continued outbreaks is to just continue informing people how much COVID is currently circulating in their community and make it just as accessible as the weather report. Because again, a lot of data suggests that people do tend to adjust their behavior accordingly. Now, will that be enough to prevent major surges? Probably not. And then, in the event of a new major variant, we will probably have to reevaluate things as well. But, as we continue to deal with COVID and we think about this sort of permanent circulation of COVID-19 on the population, I think that recognizing that there’s going to be different sorts of dynamics in different places, different patterns of spread across the year, the timing will look different. But because of that, making clear what’s happening in any given community at any given time using passive surveillance is probably the best thing we can do right now.

Q: Thank you.

MODERATOR: Next question.

Q: Thank you for taking my question. Just about the BA.2. In some countries, the increase of BA.2. corresponds to the surge of cases. But, in other countries we are not. And so, what do you think makes the difference, such as behavior or existing immunity? And also, I want to ask… What is the most cost effective or socially acceptable policy to mitigate or prevent future such? Thank you.

STEPHEN KISSLER: Great, thanks. So, I think that, we’re still trying to understand what exactly is causing a surge in BA.2. in some countries versus not in others. I do think that it probably does come down mostly to differences in behavior and differences in immunity. One of the interesting things about this pandemic is that I think it’s bringing to the fore a lot of things that we’ve also known to be true about other infectious diseases. And so, in that, you can have pretty vastly different rates of transmission in different locations of very similar viruses, and they might be locations that resemble one another fairly closely. I’m thinking of the spread of the bacteria that causes strep throat and other streptococcal bacteria can look very different in the U.S. and the U.K. We have very different variants that spread at different times. And, it’s not immediately clear why that’s always the case. It probably, again, comes down to differences in behavior and differences in immunity. So, thinking about the SARS-CoV-2 case, I’m not terribly surprised that we’re seeing very different scenarios in different countries. But, I think the question is why. So, the things that come to the forefront of my mind is that, in many places, including the United States, but certainly many other countries across the world, behavior really has changed pretty substantially since the start of the year. After we learned that for people who are vaccinated and boosted or have had multiple previous exposures to SARS-CoV-2, Omicron does not seem to be as individually severe as Delta, for example. Now, of course, that’s not true for people who have low levels of underlying immunity, where Omnicron can still continue to be extremely severe. And, Omicron is still a formidable virus. But, because of the relative lower severity of Omicron relative to Delta for people who have a lot of previous exposures, I think people are changing their behavior. And so, we’re seeing a lot more mixing that’s leading to a lot of surges in some cases. And then, I think that it may well be that the specific sub variant of Omicron that you were infected with prior to the BA.2 surge may affect your immunity to the current surge as well. We’re still trying to disentangle some of that as well, but the amount of Omincron circulation that you’ve had, as well as the specific sublineages that circulated, may contribute to how much spread we see of BA.2 as we go forward. So, it really is a combination of behavior and an immunity to the virus itself. I think it’s worth noting that we have had introductions of BA.2. to the United States and in many other countries for quite some time, and they’re really only taking off now. And so, what that suggests to me is that there really does have to be some behavioral element that allows BA.2 to spread. That just the presence of BA.2 is not enough to cause a major surge. So all of that is to say, I can’t really predict what’s going to happen in any given location, but I think that there are reasons that we’re starting to disentangle from why we’re starting to see very different experiences with BA.2. in different places. The last thing you asked about was socially acceptable ways of mitigating the spread of the virus. And, I think that all of the interventions that that we’ve been thinking about for the last couple of years really hold here. It seems like they’re just as effective BA.2. as against the Omicron variant, other sublineages of Omincron. So, again, masking and distancing, and moving encounters outside to the extent that we’re able to seem to be among the best things that we can do.

Q: Thank you so much.

MODERATOR: Next question.

Q: Thanks for having me. So this week or last week, the CDC put out a report that said that Black Americans were four times more likely to be hospitalized than white Americans for COVID. I’m wondering if you can talk to any sort of factors that may have been behind that rate and what measures can bring that ratio down?

STEPHEN KISSLER: Yeah, thanks. So, I am not an expert in this area, in sort of the divisions, the demographic divisions and especially the racial ethnic divisions in COVID-19 severity. But, it’s true that over the course of the entire pandemic, Black Americans in particular, have really borne the brunt of this virus. The one area here that I can speak to is that earlier on in the pandemic, the research group that I’m a part of did a study to try to understand part of this, of why certain communities, and we were looking in particular in New York City, why certain communities tended to have much higher rates of hospitalization and death. So, you could imagine part of it might be due to intrinsic factors of higher rates of comorbidities, which can absolutely be in play. And now, that we have the development of vaccines, it could be different rates of underlying immunity or different vaccination rates, although at that time vaccines were not available. So, one thing is basically the risk of severe illness after getting infected, but the other is just the risk of getting infected in the first place. And one of the things that we found was that… One of the big drivers of the disparities that we saw in COVID-19 outcomes across geographic locations that actually map pretty closely with differences in racial ethnic groups was attributable to differences in infection rates. So, part of it was just due to the fact that Black Americans, in particular, were getting infected a lot more frequently, in large part because they were working in occupations that didn’t allow them to protect themselves or that weren’t providing them the means to get that protection. And so, I would not be surprised if a lot of this difference is actually due to these enduring structural issues that make it such that Black Americans, in particular, remain at higher risk of getting infected in the first place. And, with those repeated exposures… Even the repeated exposures build up your immunity, it also puts you at greater risk of getting infected. And each time you get infected, there is some risk of that infection being severe. So, I’m certain that there are probably a lot of other factors that other people who are better versed in this field can speak to. But, I do know that, at least for certain parts of the pandemic, a large part of this disparity is down to just who’s getting infected. And so, I think we can still go a long way towards reducing transmission in those population groups that are most vulnerable.

Q: Thank you.

MODERATOR: We do have some folks I believe could talk to you more in depth about that. So, if you’d like to send me an email, I can connect you with those people.

Q: Awesome. Thanks so much.

MODERATOR: Sure. It looks like we don’t have any other questions right now, but I have one that was emailed to me. So if anybody’s mulling things over, I’m going to ask this one, and then we can get back to anybody else who may have a question. She said, “Should people be waiting on CDC guidance to get ahead of surges or intimations of surges that seem to be happening now in other countries or start taking action now, like putting masks back on and giving up indoor dining? And is there enough sequencing going on to attribute rising rates to BA.2 specifically?”

STEPHEN KISSLER: Yeah. I think that, in my mind, one of the things that the CDC can do well is to provide a sort of a national snapshot of what’s happening with the spread of SARS-CoV-2. But, as we were talking about before, there can be so much difference in the timing and severity of outbreaks and given locations that… For what an individual person in a specific community might need to do, the CDC may not always be the best place to look for that. I think that looking at more local surveillance platforms, many states and even many cities continue to maintain their SARS-CoV-2 dashboards. My hope is that those will continue, so that people can get a sense of how much transmission is happening in their community. In my mind, those are the sorts of things that will help us understand whether it makes sense to start masking up again and, again, think about some of the other interventions that we’ve been talking about. To be clear, I am still masking when I go to grocery stores and when I’m in places that are crowded, where the absence of a mask would not really enhance my life very much. So, generally having unmasked encounters with friends and such. But, I don’t really see the value of going to the grocery store while unmasked personally, and so I’ve just been keeping it on, especially as we’re starting to face these rising cases of BA.2 relative to other variants in the Northeast. So, I think part of it too is just trying to understand what a person’s tolerance is for these kinds of interventions and recognizing that every little bit helps. That’s one side of things. The other was to what extent can we know how much BA.2 is actually circulating? Here in the U.S., we’ve come a very long way in terms of how much sequencing we’re doing, so we have a much better sense of the breakdown of infections by variants. At this point, we can actually be pretty confident that many of the cases that we’re starting to see across the U.S., and in fact a majority of the cases that we’re seeing in the Northeast and in some parts of California, are attributable to BA.2. BA.2 is associated with some of the surges that we’re seeing in some of the prolongation of this tail of the Omicron wave that we’re seeing. Although, being associated with it is also a different question as to whether it’s the sole cause of these increases in cases, and we’ve already spoken some about how behavior in previous immunity can also affect some of these things in some complex ways. But, certainly, it is true that BA.2 is… The fraction of cases that are caused by BA.2 is increasing, and we have a very good sense of that across the U.S.

Q: Thank you.

MODERATOR: Next question.

Q: Sorry to double dip, but I thought I’d take advantage. I was wondering… In this month is the two year anniversary of the pandemic declaration and I was just wondering if you could say anything in a general way about how modeling has come along or what you’ve learned? Are you guys any better at this now and how?

STEPHEN KISSLER: Yeah, thanks. We’ve learned a lot, for sure, about modeling over the course of the pandemic. The single most important thing, in my mind, that has happened, for modeling during the pandemic, is that we’ve managed to break out of a lot of preexisting silos and to begin working very closely with people in other related fields, but that previously we might not have seen as so related. So, I’m thinking about economists and behavioral scientists and ethicists, all of whom we really could have in many ways should have been working with much more closely before the pandemic. But now, that work is a lot more integrated. And so, that reflects in the models that we built because they are a lot more mindful of real human behavior. We’ve managed to understand how people behave in the context of an epidemic much better. We’ve been able to account for those in our models. We’ve been able to account for not just the health impact, but also the economic impact of different interventions in models. And, I think all of that has been really critical for making the models speak to the current moment. So, yes, I think that, certainly, the models have improved and that is really reflective of a broader collaboration amongst scientists and amongst stakeholders in the community as well, that have helped to make the models a lot more comprehensive, a lot more accurate, and ultimately a lot more relevant to the societies they’re aiming to serve.

Q: And is it fair to say that I understand that understanding of human behavior is one of the key things that come out of our experience here that the models did look… The ones I saw back in March 2020 were these sort of tinker toys, are not of this, gives you this line. But, that really wasn’t taking into account how many people buy their mobile phone usage actually stopped going to the mall, which sounds like the kind of thing you’re talking about now that role of human behavior in shaping the course of the pandemic.

STEPHEN KISSLER: Yes, exactly. And, a lot of the models early in the pandemic were… Much of that simplicity was just driven by the lack of data at that point where we just haven’t really been able to observe how people would respond to the pandemic for long enough at that point. But you’re right, and I think the biggest thing, to distill all of that, is this greater appreciation and this greater ability to think about human behavior in a much more nuanced way.

Q: Thank you very much.


MODERATOR: All right. And does anyone else have a question?

Q: Sorry, I’ll just get one more in here, if we’re out of questions. So a question that I have is about this pre-built up sort of immunity that we’ve talked about. And you know that you were probably likely to get some protection from from the most recent Omincron wave, but do we know how much a a delta infection from last July would protect someone now? Or is there sort of like a lot of… What are sort of the knowns versus unknowns in that population level immunity?

STEPHEN KISSLER: There are more unknowns than knows, for sure, because there are so many different ways that a person could have acquired their immunity. And, in a lot of cases, it’s not very, very well documented. So, we have a decent sense of who’s been vaccinated with what and when. But when it comes to previous infections, it’s really hard to know whether a person got infected, when that infection occurred, and what it was with. That really does complicate things. But from a broader perspective, one of the things that seems to be the case is that repeated exposures to SARS-CoV-2, especially through vaccination, but also through previous infection, enhance your immunity, and they enhance not only the amount of immunity that you have, but also the breadth of the immunity that you have. So, your ability to identify other sorts of viruses. This is one of the reasons why the booster was so important for the Omicron wave is that getting that booster basically… Even though it was exposing your immune system to something that looked like the original SARS-CoV-2 variants from back in March, April of 2020, nevertheless, that additional exposure helped your immune system to see other parts of the viral spike that it may not have caught on the first time around, broadens its immune response, and allows it to better recognize something like Omicron, even though it hasn’t seen it before. So, my sense is that something like a previous delta infection would do something similar to that. I think that Omicron is about as different from Delta. Delta and Omnicron differ pretty substantially. But, nevertheless, everything that I’ve seen is that the closer, the better in terms of exposure and immunity, but still very distant things can give you quite a bit of immunity, cross-immunity to variants that are fairly different from one another. All of that is made more complicated by the fact that immunity does also seem to wane over time. So, a Delta infection from last year, for example, would have boosted your immunity to Omicron currently, but it’s also been declining. So, a Delta infection… I don’t know from November of last year would probably provide you more immunity than a delta infection from earlier in the year. So, there are all of these different forces moving in different directions, but I think the most important thing here is that, so far, from what we can tell any immunity against SARS-CoV-2 helps your immunity against any SARS-CoV-2 that you’re exposed to, and that immunity declines over time. And, the closer the thing is that you’ve been exposed to that you’re trying to face that next is better… the similarity is good, but distance is not necessarily really bad. Does that help?

Q: Yes, it does. Thank you.

MODERATOR: Thanks. All right. Do we have any other questions out there?

Q: Yes, I have a question about vaccines. There have been some reports about the impressive durability of the JNJ vaccine, even though it’s no longer recommended by the CDC here in the United States. Do you have any sense of why the durability might be better for that particular vaccine, since you were just speaking about the durability of protection from natural infection?

STEPHEN KISSLER: I don’t, and this would be a question for an immunologist. I’ve seen that data as well, and it does seem that there is some enhanced durability. And, my sense is that it probably just has to do with the way the immune system interacts with the specific thing that it’s been exposed to. Certainly, JNJ uses a different vaccine platform, and, because of that, maybe the immune system just gets triggered in a different way or different arms of the immune system get triggered. There are different parts of the immune system that lead to different durations of immunity. So really, when we’re training our immune system against the virus by vaccination, we’re really trying to train this… I sort of see our immune system as this very complex thing that has a lot of different agents that act to clear viruses in a lot of different ways. And some vaccines really get it exciting one part of the immune response, but they don’t really do much to a different part of the immune response and vice versa. So, I think it really just comes down to that balance of the response of which parts of the immune system got triggered by the vaccine. That’s a really difficult thing to tell from the outset in initial vaccine trials, because our understanding of the immune system is still very much… We know a lot, but there’s a lot left to learn. I think that’s probably the best I can do and maybe referring you to an immunologist would be the next thing.

Q: Thank you.

MODERATOR: Any other questions? Looks like maybe not. Dr. Kissler, do you have any final thoughts for us?

STEPHEN KISSLER: No, I think you’ve sapped just about all my information today, so thanks.

This concludes the March 23rd press conference.

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