Why Does COVID-19 Spike In Summer?

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky.

It seems like everyone’s either coming down with COVID this summer or perhaps knows somebody who is. And that’s because, for the fourth summer in a row, COVID cases are once again experiencing a summer surge.

Now, the CDC tracks COVID mostly through wastewater. And viral activity has multiplied more than four times from the beginning of May until now. The CDC classifies this viral activity as “a high level.” So what’s behind this surge, and why does it keep happening each summer?

Joining me now is Jessica Malaty Rivera, infectious disease epidemiologist and science communicator at the de Beaumont Foundation, based in San Francisco. Jessica, welcome back to Science Friday.

JESSICA MALATY RIVERA: Thanks for having me, John.

JOHN DANKOSKY: OK. So it does seem like everyone I know is out sick this summer. What exactly is behind this big summer surge?

JESSICA MALATY RIVERA: Yeah, as you said, I mean, this is our fourth summer with COVID-19 and it is our fourth summer with a COVID-19 surge. And it’s pretty predictable because of a few things– three mainly. One of them is behavioral. So in the summer months, it’s a lot hotter, and people are trying to escape the heat and going inside, where they have access to air conditioning. People are traveling and going on vacation. People are doing a lot of large gatherings and parties and celebrations. And so some of that is just part of summer behavior.

The second thing is the virus is changing. As the virus continues to evolve, it mutates. And these mutations give it a adaptation to be better at attacking your immune system, better at causing an infection. And then the third thing is it’s our waning immunity. Probably been a while for folks who have either been previously infected or previously vaccinated. And the longer that time goes, the more susceptible they can become to getting a new COVID infection. So there’s a lot of things that make this a bit predictable.

JOHN DANKOSKY: Yeah, it is seemingly predictable. Now, how exactly is this summer comparing to the last few?

JESSICA MALATY RIVERA: This summer is pretty high. And that’s based on wastewater data, as you mentioned. But we’re not looking at it with the same type of data as we have in previous years. As you know, we don’t have the same kind of access to testing data and to case data in previous years because of the reduction in COVID data availability. That said, when you look at it compared to hospitalizations, which has historically been the closest to real-time data that we’ve ever had during the pandemic, hospitalizations are increasing. But they’re not at the same rate or as high as previous rates in summers in the past. Which is a good thing.

There’s a couple of things that can explain that. Part of that is people’s population immunity. Folks are more protected against COVID than they have been in previous years. And so there aren’t as many hospitalizations and deaths. But it is still on the uptick, which is why we are on alert right now.

JOHN DANKOSKY: One of the things that you’ve mentioned, of course, is the mutations. Let’s talk about the variant that is currently circulating the most. It’s called FLiRT. What can you tell us about it, and is there anything special about this particular variant?

JESSICA MALATY RIVERA: There is KP.2, KP.1.1, and KP.3. These are all considered the FLiRT variants. KP.3 is the new Omicron sub-variant, which, along with KP.2, has been the one that’s probably the one responsible for the most COVID-19 infections, based on wastewater data. These have been gaining traction in the last several months. And they’re still doing a lot of genomic surveillance to see how this virus is evolving. And just like in previous ones, they gain dominance as people’s previous immunity wanes. So these are mutations that make the virus better at attacking your immune system, better at causing an infection.

But it’s kind of the same situation– there is nothing that is dramatically different about the virus. It is still COVID-19 is the disease that it causes. It just is happening quicker. The mutations are happening at a quicker rate than we are seeing in other viruses like influenza, which makes it why we are seeing it behave in a non-seasonal way.

JOHN DANKOSKY: Why exactly are we seeing these mutations happen so quickly?

JESSICA MALATY RIVERA: Again, this is one of the reasons why we say COVID-19 is not the flu. It is not like the flu. It doesn’t behave in the seasonal way like flu. It doesn’t mutate at a rate like flu does. I mean, flu mutates at a much slower rate, which is why we see it happen annually.

There are a lot of reasons for that. Part of that is just where the mutations are happening on the virus itself. But again, the virus is not dramatically changing in what it’s able to do in the body, which is a good thing. It’s still causing the same type of disease, but with the complications of long COVID still looming, of course.

JOHN DANKOSKY: Just a minute ago, you also mentioned that our waning immunity is playing into the summer surge. I don’t know about you. It’s been a little while since I last got a booster shot. How often should people be getting boosters? And what kind of booster?

JESSICA MALATY RIVERA: Yeah, that’s a great question. So previously, we were doing a bit of variant chasing and updating the vaccines, but uptick for those vaccines was not great. And I understand that there’s a lot of human fatigue in that. It’s just a lot to ask people to get vaccinated multiple times a year, which is why they switched to an annual cadence, to follow along with the flu vaccine timeline, despite the fact that it doesn’t behave seasonally like flu. It just seemed like we probably have the highest rate of success when it comes to getting those people vaccinated. And it is going to be probably a few more weeks till we see the updated vaccine available.

For folks who have not been infected for a while and have not been vaccinated for a while, this is a particularly vulnerable time– waiting for that new vaccine to be available. That said, folks who are considered high risk and immunocompromised are encouraged to vaccinate at a different cadence– more like every six months– so twice a year. But for the rest of us, who are generally healthy and not at high risk, we’re having to wait until the fall of every year to get that new updated vaccine.

JOHN DANKOSKY: So you talked about the vaccine fatigue that many people have after several years since the pandemic first broke out. Here’s a couple of different reactions that I periodically get. One is, well, COVID is over, for the most part. I just don’t need vaccines anymore. Some people are saying, well, I got all my vaccines. I have all my boosters, and we’re still in this mess. We still have people getting COVID. So how do you respond to people who have either of these kind of polar ideas about how they should react to this?

JESSICA MALATY RIVERA: Yeah. I mean, it’s tough. And I empathize with folks who are over COVID-19. I very much want to be over COVID-19, even though COVID-19 is not over us.

JOHN DANKOSKY: I’ll bet.

JESSICA MALATY RIVERA: And this is the complication of a virus that has become so well established, not only among humans, but among other animal species, making it impossible to be fully behind us. That means COVID-19 is endemic. It’s going to be in our human population for the foreseeable future. And it’s likely that it will be around for a very, very, very long time. And so learning to live with COVID is going to require a little bit of flexibility from folks. It’s going to continue to be disruptive. It’s going to continue to cause infections. It’s going to continue to cause plans to get canceled.

And our best ways to reduce that burden are to get vaccinated, to reduce the risk of those severe outcomes, and even to use those non-pharmaceutical interventions that we’ve been talking about for four years and counting now– wearing masks, staying home when you’re sick, testing if you feel sick, and isolating and quarantining for the proper amount of time.

JOHN DANKOSKY: Originally, during the first COVID surge several years ago, there was a thought that things would wane in the summertime because people can go outside and be in the fresh air. But with the incredibly hot summers that we’ve had in many parts of the United States, people are coming inside to cool down from the heat. So what do you tell people in terms of staying safe in situations where being in the air conditioning is actually keeping them safe from really hot conditions outside?

JESSICA MALATY RIVERA: Yeah, it’s challenging because climate change is not too far off from the world of infectious diseases. In fact, I would say that the increase in climate change and increase in global temperatures is a driving indicator for us being exposed to new viruses that we don’t have immunity to. And so caring for our climate is very much a public health issue.

And to care for folks who are experiencing extreme temperature, I mean, obviously they need to stay cool and stay inside. And the safest way to do that, if you feel like it is a high-risk situation where there are a lot of people indoors and a lot of people who might be sick indoors, is to wear a mask indoors. I still wear a mask when I’m traveling. I still wear a mask on airplanes. I wear a mask whenever I feel like there’s just too many people around. And that’s probably the best way– that and getting vaccinated– to survive both the heat and being indoors during a COVID surge.

JOHN DANKOSKY: But I think that a lot of the problem is that, as you said, the guidance has changed. The federal government isn’t paying for the same things they were paying for before. There’s not a sense that you have to mask when you go places. And so many people just choose not to. From a public health perspective, how do you think that we should be thinking about this– tackling this at this moment– where clearly there’s a surge, and clearly some of that behavior that we’ve put aside would really help in keeping from spreading this disease?

JESSICA MALATY RIVERA: Yeah, it’s a very fair point. I mean, politics very much influences public health. And we recently saw President Biden, who tested positive for COVID, go unmasked the next day around his Secret Service officers. So it just shows there’s a general behavioral and attitude shift around COVID-19. And if we can’t look to leaders for leading by example, we can still look to the science that says that masks do work to reduce transmission, that vaccines work to reduce severe outcomes, that staying home when you’re sick is the best thing you can do.

And so we still have a lot of public health lessons that people can continue to adopt that didn’t age out because of COVID-19. Masking is not a new phenomenon. Masking existed prior to COVID-19, and is a part of a lot of people’s new muscle memory. We keep them by our door at our house just in case we’re going to be someplace that we think we might need to grab a mask and head out for that. So I don’t think that just because the public health emergency has ended or because it’s not being mandated that people should think that the COVID-19 pandemic is over or behind us. We’re still dealing with it. And this is not to sound alarmist, but there are still things that we can do to reduce harm and to reduce risk.

I also understand that it is a bit of a financial burden for folks, too, to have to pay out of pocket for masks and pay out of pocket for tests. And so, as they are accessible, to try to use those mitigation efforts as best as possible would be great.

JOHN DANKOSKY: Let’s look ahead toward next summer, if we could, just because we’re sitting here talking to you again in another summer in which we have a summertime surge. It seems, Jessica, as though– I don’t know– perhaps we may have learned something, and we would like to try to keep this from happening next year. So let’s look into a crystal ball and try to figure out what exactly will the United States have done by 2025 to keep this from happening again next summer.

JESSICA MALATY RIVERA: This is a tough question to answer, and I’ll say two things. I would hope, on the behavioral side, that folks would learn to anticipate a summer surge. And because of that, they would learn to make sure that they are keeping their risk low, whether that’s through masking or staying up to date on their vaccines or making sure that they stay home if they’re sick, or maybe changing their activities to be more indoors as the climate allows.

And then, on the viral side, it’s just to be expected, right? If this virus truly is endemic and will continue to mutate and adapt, we know that it’s going to happen. But hopefully, by then, our behavior will allow us to prevent some of those infections that seem to be very predictable at this point.

JOHN DANKOSKY: I’d like to get back to the monitoring that you’ve been talking about. Several times you’ve mentioned the fact that the data that we have really is from wastewater treatment plants. We’re getting different types of data than we used to get. How big a deal is it that we don’t track COVID the same way that we did a few years ago?

JESSICA MALATY RIVERA: It’s a very big deal. And you’re talking to somebody who’s an alum of the COVID Tracking Project, which was a mostly volunteer effort of 800 people, who tracked daily case testing, hospitalization, and death data for 50 states and six jurisdictions. And it was a full-time job for almost two years. I mean, we would spend between 15- to 20-hour days doing this type of poring over the data, making sure that we had as close to a big and clear picture of the data. And even still, it wasn’t enough. And that was when we had the most data available.

Right now, we’ve got a lot of blind spots. Hospitalization data that is available on the CDC website is coming out of only 13 states. And so they’re providing rates per 100,000 people and then extrapolating that data for the rest of the country. It’s really difficult to get a full understanding because hospitals are no longer compelled to submit that data.

Death data has a huge lag. And we know that for the time it takes to process that information. And right now, most of the testing data is in people’s trash cans across America because that’s not being submitted to dashboards or to databases that are then being published. And so it’s very difficult to rely on something like just wastewater or a little indicator of hospitalization data from a subset of states in the United States. It’s really difficult.

JOHN DANKOSKY: I think another thing that has changed, too, in terms of public policy, this is the first big wave since the CDC updated the COVID guidance back in March. It, as you said, rolled back protections. It loosened up some rules. There was a lot of controversy at that time about that change. How exactly has that panned out? What do we know?

JESSICA MALATY RIVERA: Yeah, it has been pretty controversial for a few reasons. Partially, like we were talking about earlier, COVID-19 and influenza are not the same. And so the grouping of the respiratory viruses– they now group COVID-19, influenza, and RSV in a respiratory virus tracker. For folks like myself, we struggle with that because we’re dealing with viruses that just don’t have the same type of seasonality. They don’t have the same type of trends or complications. And it makes it difficult to separate the data and really understand the unique challenges of COVID-19.

COVID-19, it was very disruptive. And to public health, it was very disruptive. And it requires a ton of resources. And I understand that there was a shift, because of resource restrictions, too, on not having to just focus on COVID-19. But that said, it means we are not looking at it with the same type of visibility. In fact, it’s worse visibility today because of these resources restrictions.

JOHN DANKOSKY: I’d love it if you could leave us with some tips for folks who may have been exposed or maybe had a loved one be exposed. They’re starting to feel sick. What exactly can they do to best stay safe, to feel better, to protect others? I mean, what if you get COVID now, Jessica?

JESSICA MALATY RIVERA: So the good news is that the available rapid antigen tests are still effective at detecting COVID-19. So if you are starting to feel sick, my recommendation is to stay home because you don’t really know what it is. It could be COVID. It could be flu. It could be any other thing that you don’t want to spread, regardless of the virus. And so if you do feel sick, I would recommend testing.

It may be a while, though, to test positive on a rapid antigen test. And that’s for some of the reasons we talked about earlier, John. Our previous immunity, it’s working to make sure that we don’t test positive. And then, eventually, sometimes that virus will take over. And it can take a few days for that to happen if it is actually COVID. So I would test for a few days while you’re symptomatic.

If you are sick or symptomatic, I would stay home. If you are mildly symptomatic and you need to get out, I would not leave without a mask. And I would definitely not do things that are with people in high-risk populations for the sake of their health and their well-being. So there’s lots of things that people can do to reduce the harm to themselves, but I would think also, in the altruism of public health, to protect other people by not putting them at risk if you do feel sick at all.

JOHN DANKOSKY: A very practical question for you. I think a lot of us still have some of those free tests that the government sent out years ago, sitting in our cabinet somewhere. If they’re outdated, do they still work?

JESSICA MALATY RIVERA: That’s a great question. So there is a spreadsheet on the FDA website that you can usually check the– I think it’s the serial number or the lot number of those tests– to see if they’ve actually extended the expiration date. I’m not sure how recently that dashboard has been updated, but the last I remember, when they sent them, they even sent it with a piece of paper that said, these are still good until– and then they had an extended expiration date from the one that was printed on the box.

JOHN DANKOSKY: Of course, we’re already in August. And so we’re heading toward fall, which means back-to-school season. What exactly should parents know before sending their kids back to school?

JESSICA MALATY RIVERA: Yeah, this is something I think about a lot. I’m a mom of three, and my kids are all going back to school in mid-August. And so I’m thinking about their flu vaccines and their updated COVID-19 vaccines, and have them scheduled for as soon as they become available in their pediatrician’s office. Masking is hard to find in some schools. In my kids’ schools, it’s actually pretty common. It’s not required, but my kids will probably be wearing masks during the fall months especially because there’s going to be a lot of bugs, a lot of flu, a lot of COVID going around, especially in those September, October months.

And so I would just stay up to date with your vaccines, with your pediatrician, and keep your kids home when they’re sick.

JOHN DANKOSKY: I hate that we have to keep talking to you each and every summer about this, but I’m glad that you’re here to give us this information, Jessica.

JESSICA MALATY RIVERA: I’m happy to be here, John, any time.

JOHN DANKOSKY: Jessica Malaty Rivera is an infectious disease epidemiologist and science communicator at the de Beaumont Foundation, based in San Francisco.