Evolution of a Pandemic: Where Does Delta Leave Us?

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Right now, Delta is the dominant COVID-19 variant spreading here in the U.S and in some other areas of the world. It’s one of the handful of variants that have evolved from the original COVID-19 virus. The emergence of the more infectious Delta, and the prospect of new variants on the horizon, has underscored the urgency of widespread vaccination to put an end to the pandemic.

In this episode, we're joined by two faculty experts from the University of Michigan who will discuss what is currently known about the Delta variant, how vaccine efforts are holding up through the Delta surge, and how it's spread is impacting our ongoing pandemic response strategies.

Listen to "The Evolution of a Pandemic: Where Does Delta Leave Us?" on Spreaker.

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0:00:04.1 Emily Martin: As cases go up in a community, the risk goes up for everybody. Risk goes up for the vaccinated, even though it's less, and risk really goes up for the unvaccinated. And so, Delta's big problem is that it pushes up rates in the community so, so fast, so then it's gonna push up cases in everybody, vaccinated and unvaccinated.


0:00:26.4 Narrator: Right now, Delta is the dominant COVID-19 variant spreading here in the US and in some other areas of the world. It's one of the handful of variants that have evolved from the original COVID-19 virus. In this episode, we'll learn more about how Delta may be changing our response to the pandemic. Hello, and welcome to Population Healthy, a podcast from the University of Michigan School of Public Health. This episode is part of a series of special editions of our podcast focusing on the ongoing Coronavirus pandemic. Jon Zelner is an Assistant Professor of Epidemiology at the University of Michigan School of Public Health. He's a social epidemiologist, focus on understanding and targeting the joint social and biological drivers of infectious disease risk. Professor Zelner joins us to talk through what is currently known about the Delta variant and how it's impacting our pandemic response strategies.

0:01:19.1 Jon Zelner: What do we know? We know it's much more infectious than the wild-type variant or the previous variants of concern that have come before, like B.1.1.7. One thing that's important to remember is that most of the cases that we see, the vast majority are in people who are unvaccinated, and that that implies doubly or triply to the hospitalized cases and deaths. We know that the vaccines are doing a good job of preventing these cases of symptomatic disease from the Delta variant. We know and should have known beforehand that there's no reason vaccinated people can't get infected. So the vaccines are protective against infection, but we got this idea, I think, in our heads, from the way it was discussed publicly and in some of the scientific discourse, that these COVID vaccines were so effective, it was as though you had no risk of infection or transmission once you're vaccinated. That's never been true for any vaccine, and it's not true for these vaccines, and so, there's this disappointment that we have these so-called breakthrough infections, but in reality, when you have lots of transmission in the community, even if it's only a small fraction of vaccinated people who'll get infected, you'll still see plenty of infections among the vaccinated. So that shouldn't necessarily deflate our confidence in the vaccines, but it should serve to temper our expectations.

0:02:40.5 JZ: So, why are we paying so much attention to this particular variant? What is it that differentiates the Delta variant from either the wild-type that we saw at the beginning the pandemic or things like the Alpha or B.1.1.7 variant? There's a couple of things at play. One is that this particular variant seems to be strongly transmissible, even relative to the Alpha variant or the wild-type. It's much more infectious than the previous ones, and that's kind of in line with how we understand viral evolution. I think the bulk of the attention, in some ways, comes from the fact that we kind of... Should have seen this coming, but didn't see it coming. We got to a place where we're thinking, "Oh, this thing is winding down. We can really kind of pull back and relax. And the vaccine coverage that we have is not perfect, but hopefully, it's good enough to keep things down." It's partially 'cause it's a novel pathogen and it's very infectious, and it's partly because there's a social component where we got into a place of thinking we were getting out of this; I certainly felt like that. And now we feel plunged back into it.

0:03:42.6 Narrator: Despite the new variant, Zelner says we should feel confident continuing the same mitigation measures against Delta as we did for the original COVID virus.

0:03:51.6 JZ: Just because you have a pathogen that's more transmissible, that seems to be a little less susceptible to the vaccines doesn't mean that everything has changed. The changes in the virus are not really at a fundamental physical level. So things like masks and social distancing are useful because they act on these kinda very basic physical properties of the virus, which can transmit via droplets and aerosols, and a mask, at the end of the day, is kind of just like a napkin that you put in front of your face, and it absorbs droplets as they come out of your mouth, and it can slow progress of aerosols as well. So they're imperfect, but they do do a tremendous amount of work, and these variants have not, so far, changed those characteristics of the virus; that would be a big leap relative to what's going on. So the viruses that we're seeing circulating right now are the same but different. That's why we kind of find ourselves reiterating the same things over and over again: Masks, distancing, etcetera. Those things still do work, but ultimately, when you have something that's more infectious, you're still gonna get transmission, and you may get more transmissions even if you are masking and distancing and all that kind of good stuff, because the pathogen itself is just inherently more infectious.


0:05:10.0 Narrator: Emily Martin is an Associate Professor of Epidemiology at the University of Michigan School of Public Health. She's been established as a leading expert on the vaccine and its rollout throughout the COVID-19 pandemic. Professor Martin says, despite the variant's spread, the vaccines continue to hold up.

0:05:26.5 EM: I wanted to take a minute and talk about the hot topic of the hour, which is vaccine effectiveness. How do we think about it, how do we know how effective our vaccine is, and what do we know from those sources? So when we say vaccine effectiveness, we're not talking about the likelihood that you get infected. What we're talking about is the percent of infections that are prevented by the vaccine. So if a community were to have 100 infections, if they have a vaccine that's 80% effective, like in this example, then 80% of those infections are stopped. If you even have a vaccine that, say... Let's take a worst case scenario and say it's 30% effective. It means that you stopped 30 out of 100 infections. And so, the effectiveness number basically tells you the percent of infections that would have occurred that you've stopped by using the vaccine.

0:06:10.9 EM: But what we are learning is that the way the vaccine prompts immunity makes your immunity more robust to changes in the virus. If you get infected, you are very protected against that one for a period of time that we're still determining, but you're [0:06:35.9] ____ protected against that variant, you may not have the breadth to get a COVID strain that's slightly different. The vaccine is still working pretty solidly against the Delta variant itself, at least at preventing hospitalizations and pretty severe disease in most people. For the Lambda variant, we're watching to see if that's gonna hold true, or if the Lambda variant and the vaccine is gonna be more of a mismatch. We're used to thinking about this from flu before. Every year, we had to figure out what strains are new, how do we make the vaccines match this? So we actually already have a way to think about how to kind of version the vaccine to be responsive to whatever is coming.

0:07:00.3 EM: The great thing about the mRNA vaccines... Actually, this was a technology that was already in development and under consideration for things like influenza because of its ability to be changed so quickly. You've got a house, and you can take just one little Lego block off of that house and make it match the new variant, and now you've got a vaccine that matches. You can do it without having to do this very long R&D process and all these sorts of things we do with the flu vaccine. And so it's a very fast vaccine to change. There's already scientific panels in place, both at the government level, at the industry level, to watch to see what changes need to be made to the vaccine. And we already have a process in place, so the same federal panel that reviewed the vaccine, the EUA, those panels are also in place to review, for instance, the annual flu vaccine changes. So we'll see those panels also be reviewing the data to say, "Okay, do we need to change the content of the vaccine, and when do we do that, and which strains do we change to?" So I'm pretty optimistic on our ability to be responsive with the mRNA vaccine.

0:08:00.0 EM: Now, as communities have more and more infection come into the community, you have more and more potential for these less likely but still... Breakthrough infections that will occur. Breakthrough cases... Most people probably are familiar with the terminology. It's talked about when you've got people who are vaccinated and were infected. So unless you have a vaccine that's 100% perfect every time in every person, you're gonna see cases in people that were vaccinated. Now, for the most part, the data is showing pretty clearly that people who are vaccinated when they're infected, the disease is less severe than if they were unvaccinated and then infected. You're going to have some breakthrough cases, but you're stopping many times, five times more cases because of the vaccinations having happened. And so that's why you hear a lot of talk about layered strategies. It's important to continue to keep community rates low and to continue putting vaccine in the community, because everybody's risk goes up when the community level goes up.


0:09:03.1 Narrator: Getting a COVID-19 vaccine remains crucial, but the Delta variant spread demonstrates why community vaccination is more likely to be the determining factor to curbing the virus's evolution.

0:09:15.3 JZ: One of the things I think really gets left out of the discussion about why it's important to get entire communities vaccinated is that when you have only part of a community covered by vaccination, you actually find yourself in kind of a dangerous situation. So every transmission event is really just another opportunity for the pathogen to find a new way through the population. Essentially, you're giving the pathogen kind of shots on goal, and you're giving it the opportunity to kinda get one or more past the goalie. You're giving the virus the opportunity to kind of check out how it might get past the defenses of vaccinated people. If we set up a situation in which, essentially, natural selection can work through this puzzle through lots of random shots at vaccinated people from infectious, unvaccinated people, that obviously sets up a very dangerous situation. And so, there's a tendency for us to think of this pandemic or epidemic as the thing that only goes down, but I think the last year and a half or more of experience have shown us that it goes up and down in response to our behavior as much as anything else, and that applies not only to opening the faucet of transmission and closing it down with our activities, but also the evolution of the pathogen.

0:10:26.8 Narrator: To deal with the formation and spread of variants, we have to start thinking beyond just vaccinating individuals, and taking into account the impacts of each stage of the pandemic on whole communities.

0:10:36.3 JZ: One area that we really don't know very much about, and I think will kind of remain to be seen, is what the impact of the Delta variant or other variants is on the picture of inequality in infection. At every stage in the pandemic, it's always been folks who are experiencing more difficult socioeconomic conditions or who are more subject to racial discrimination, who get the short end of transmission, and there's no real reason to expect that that would be different with each successive variant, but I think the contours of that and how it kind of lines up with vaccination and of transmission, I think, remains to be seen. One thing that's really important to remember is that infectiousness isn't just something that's a property of a pathogen. So certainly, the Delta variant is different biologically than the wild-type variant and the ones that have come before it, and that difference has an important impact on its infectiousness, but there are other factors that have as much or more of an impact on transmission in different contexts.

0:11:35.9 JZ: So certainly, we've seen in jails and prisons that the high density of folks in there is an ideal environment for transmission of this pathogen, and probably, that effect only is amplified in the context of Delta, but the social conditions are as or more important. And similarly, things like overcrowded housing is something that kind of modulates transmission for the same reasons. The kinds of jobs that people are forced to work that may put them at risk, whether that's working in a food service context, where there's lots of contact with the public, who may or may not be willing or interested to be masked or vaccinated or what have you. So ultimately, your transmission risk comes down to this cocktail of the infectiousness of the pathogen that you're confronted with, and also the social context in which that transmission Is occuring.


0:12:27.4 JZ: One thing that I think we've seen play out a number of times is people really pushing on this idea that there's some other person or set of people out there who's doing the wrong thing, when good, like-minded people such as ourselves are doing the right thing. It's important to work past this if we're going to actually have an effective response to what's going on. Part of that is stuff that's pretty hard to address in the present moment. It requires kind of broad scale political change, and it requires a kind of coalition-building across social and political groups that doesn't just kind of sort people into "These are the anti-vaccine people, these are the folks who are unwilling to wear masks." It's much broader than that, and I think it comes down to kind of understanding that there's a set of kind of powerful interests that you would expect would be aligned in a way where everybody would say, "Yeah, what we care about is reducing risk for people in the population as a whole and getting this thing under control," but it turns out that the pandemic as it exists, in some ways, is quite profitable for certain sectors of the economy. Thinking things like Amazon, thinking about things like cable news...

0:13:37.2 JZ: So there are kind of malefactors out there who are doing quite well off the back of this, and I think that that's a big part of the story about why we constantly talk about one group of people who's vaccine-hesitant. We obsess about the news story about some people taking cattle dewormer instead of taking vaccines, and on the face of it, it's like, that's silly and dangerous and all that, but that's not very many people, but that comes to define the debate. And I think most of the people who aren't vaccinated aren't for a wide variety of reasons. Some of them are truly hesitant, some of them are believing in a conspiracy theory, some of them have issues with access, where it just is not available in a reasonable distance from where they are, or they can't take time off work, or they have a tenuous immigration status... And so, there are many reasons that, suddenly, these things have not worked, and I think we have a tendency, certainly in the US, to boil everything down to individual behavior, individual opinions, and obviously, individual behavior has a role to play, but you can't have something go this badly wrong, on this kind of a scale, and be able to just blame individual people for it.


0:14:47.7 JZ: One story that we hear over and over again is about this concept of vaccine hesitancy, and how there are these folks who are scared to get the vaccine, either due to misinformation about the effectiveness or safety of the vaccines, or because of kind of historical concerns about medical experimentation on racial and ethnic minorities, particularly African-Americans, and obviously, those are real concerns that people have, of varying degrees of validity. But there's another part that I think is really important, which is that the vaccines were trotted out as something that were free and effective to an extent that was almost unheard of, in terms of the things we talk about in public health prior to this, and as being completely safe. And what else in American healthcare is certainly free? 

0:15:35.4 JZ: But I think that point of something being free is something that can kinda set off alarm bells in a lot of people, particularly those folks who are excluded from the healthcare system, who don't have health insurance to begin with, and for whom the idea of just being able to walk in and get what is essentially kind of life-saving preventive care at no cost is kind of alien. If something looks too good to be true, maybe it is. And obviously, I don't believe that that's the case with respect to the vaccines, but I think the idea that "We'll give you this for free, this thing is really important, but everything else is kinda off-limits" is kind of hard to swallow. Ultimately, it just highlights the kinda cruelty of our whole healthcare system. And so, I think we're not gonna fix this problem unless we make wholesale changes to the way we think about who gets care, who deserves care, and what the implications are of that formulation for us as a society. I think, as much as anything else, the kind of widespread hesitancy or pushback represents those failures more than, again, the failures of individual people to do the right thing.

0:16:39.3 Narrator: There was a lot of optimism and collective relaxing this past spring, but into summer, as Delta emerged and spread, we witnessed just how quickly things can change. Now a key question is, what can we expect going into fall? 

0:16:51.4 JZ: Going into the fall, I'm hopeful that we're gonna see the rates, certainly for Delta, to come down. It's anybody's guess what's gonna happen as the weather turns and people sorta find themselves inside... In a kind of climate environment that may be a little more conducive to transmission. One, if you wanna call it, a positive upshot of what's been going on with the uncontrolled Delta transmission in many places is that there has been a significant uptick in the rates of vaccination in places like Florida, Texas, Alabama, and I think a lot of it is coming from people seeing friends, family, neighbors getting sick and dying, and that really resonating on a level that all this other messaging really couldn't. That tells you kind of what we're up against, that it takes this kind of extreme event to kinda move the needle. And ultimately, I think that what that boils down to is, it's only the things that move you emotionally that are going to move you to make a change in your behavior.

0:17:48.6 JZ: And so, for those of us who were kind of primed to be concerned about the pandemic and to believe that there were interventions coming that could help us, I think we were able to kind of come along on that emotional journey. For folks who've been kind of left out of that, for political reasons or for cultural reasons, like they're in whatever particular bubble you're in, I think we're seeing how hard it is to pierce that, but that hopefully, some of it has gotten through and is going to make the difference, and I certainly don't wish the things that have happened on anybody, but I think that sometimes, the only way to move the needle is through experience.


0:18:27.4 JZ: It's important to remember that we can still get past this particular hump, and I think the thing that's demoralizing is the idea that every time we kinda get past one event in this, we wanna convince ourselves that it's over, and I'm certainly susceptible to that kind of thinking as well. But I think the sooner we accept the idea that we're on the downhill, but there's gonna be kind of some bumps along the way, and that there will be bumps to come, I think we'll be better prepared, not only to kind of wind down this particular moment, but also to be prepared for what comes next.


0:19:08.1 Narrator: This has been a special edition of Population Healthy, a podcast from the University of Michigan School of Public Health. During the ongoing Coronavirus pandemic, we'll work to bring you analysis from our community of experts to help you understand what this public health crisis means for you. To stay up-to-date inbetween special edition episodes, be sure to check out our website, publichealth.umich.edu, subscribe to our Population Healthy newsletter at publichealth.umich.edu/news/newsletter, and follow us on Twitter, Instagram, and Facebook at umichsph.

In This Episode

Assistant Professor of Epidemiology at the University of Michigan School of Public Health

Jon Zelner is a social epidemiologist focused on understanding and targeting the joint social and biological drivers of infectious disease risk. His work blends theory and methods from sociology and epidemiology, with an emphasis on the development and use of novel computational and statistical methods for integrating social and biological data. Learn more.

Associate Professor of Epidemiology at the University of Michigan School of Public Health

Dr. Martin’s research focuses on respiratory virus epidemiology, hospital epidemiology, infection prevention and molecular epidemiology. She and Monto co-lead the Michigan influenza Center, one of five centers across the country that collects data for the Centers for Disease Control and Prevention. Learn more.