Why Are Flu And Other Viral Infection Rates So High This Year?

Flu infections are the highest they’ve been in nearly 30 years, and flu deaths this winter have surpassed COVID deaths. What’s going on?

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:18Flora Lichtman?

  This is Science Friday. I'm Flora Lichtman. Today in the podcast, we're digging into some viral trends.

• 0:24Speaker 02

  You know, this winter, we had a very small COVID wave. There's this hypothesis that because we're having such a big flu season, these flu cases are pushing COVID aside.

• 0:40Flora Lichtman?

  It has felt like a brutal season for sickness. More people have gotten hit with flu symptoms this year than in decades. Hospitalization rates are the highest they've been in 15 years. And on top of that, norovirus is retching new highs. There's been a surge in walking pneumonia cases. Of course, there's RSV and COVID, and now concerns about bird flu. It's a lot to worry about. So is this year, in fact, very viracy? And if so, why? Joining me now to explain are my guests, Dr. Kaitlin Jetalina, epidemiologist and author of the newsletter, Your Local Epidemiologist. She's based in San Diego, California. And Dr. Erica Shinoy, chief of infection control

• 1:23Flora Lichtman?

  at Mass. General Brigham, based in Boston, Massachusetts. Okay, Kaitlin, is it me, or is it actually an unusually bad year for viruses?

• 1:32Speaker 02

  No, it is not you. There's a lot of sick people out there. Like you mentioned, influenza-like illnesses, which is about fever, cough, runny nose, haven't reached these heights since the 1990s. And the main culprit is flu. Flu usually gives us a roller coaster because of changing weather and different strains. But as of now, flu hospitalization rates are higher so far this season than any time during the past 15 years. And interestingly, this is also the first winter that flu deaths passed COVID deaths. So it's definitely palpable out there, and a lot of people are feeling it.

• 2:11Flora Lichtman?

  Okay, why is it such a bad year for the flu?

• 2:14Speaker 02

  You know, a nasty flu season. It's usually due to a few different factors. One is that it just could be a bad flu year. It happens every couple of years because of waning population immunity. Second is fewer kids are getting vaccinated against the flu than in pre-pandemic times. The latest numbers are about 44% of kiddos are vaccinated for the flu. This is compared to 58% in 2019. And the third reason is just the match between the flu virus that is circulating and the vaccine is just OK. One of the strains that's circulating is H3N1.

• 2:53Speaker 02

  And that is just a notorious strain that our flu vaccines have a hard time targeting. So because of all of that, we are seeing severe disease on a population level.

• 3:06Flora Lichtman?

  Erica, tell us about what you've been seeing at your hospital.

• 3:09Speaker 03

  So we've seen basically a replication of the national data in terms of the number of flu cases in hospitalizations. I do think it, at least in my professional career, this hearkens back to 2017 and 18, which was, prior to this one, a pretty severe flu season. Additionally, the number of influenza tests that have been reported to the CDC is much higher than in prior years. At the hospital, I see a little bit of glimmer of hope, just based on some of the more recent numbers that we're seeing. The CDC data is delayed by a little bit, but in terms of our daily numbers of flu cases and patients being admitted to the hospital with flu, I think we may be close to the plateau.

• 3:53Speaker 03

  I never want to, like, you know, use a crystal ball, but there are several things, including wastewater data, that seem to make it seem like we're headed towards potentially the peak, and then we'll have to make our way down that.

• 4:05Flora Lichtman?

  That tall, tall mountain, yeah. I mean, how has it been in the hospital? Has it have these higher rates of flu and flu-like illness made the hospital more crowded? You know, what are the effects of that for you on the ground?

• 4:21Speaker 03

  Well, we were definitely experiencing even prior to COVID, extreme capacity, very busy emergency rooms. So additional influenza activity, a severe season obviously puts additional strain. So I would say that on a hospital level, when you're operating at really the margins in terms of capacity, that that having a severe flu season has strained across the board. We're making our way through it like we do every year and in trying to make sure that people are aware of their options, getting treatment early so that they can avoid hospitalization.

• 4:55Flora Lichtman?

  Caitlin, you mentioned that flu deaths surpassed COVID deaths for the first time since the onset of the pandemic. Does that tell us anything about the COVID virus or how it's evolving?

• 5:09Speaker 02

  I mean, I think that's the billion dollar question. And honestly, we just don't know. You know, this winter, we had a very small COVID wave. In fact, the smallest since COVID first came on scene. And this could be due to several things. One is we just had a pretty big COVID wave during the summer. And so population immunity built up over time. And so that's preventing some infections. COVID also hasn't really mutated in a big way to escape our immunity. It's still making small incremental changes, but not these huge jumps like we saw from like Delta or Omicron, for example.

• 5:50Speaker 02

  The third thing that I think is most interestingly, I'll put my geekiness hat on, is that there's this hypothesis that because we're having such a big flu season, these flu cases are pushing COVID aside. And so will COVID reemerge when flu goes down? Is COVID really turning into more of its cousins, like these coronaviruses that are just become the common cold after we've built so much immunity? I mean, these are a lot of questions we just don't have answers to yet.

• 6:26Flora Lichtman?

  When you say pushing COVID aside, like the flu's out competing COVID? If we're the ecosystem, they're, they're, they're colonizing us and there's no room for COVID?

• 6:35Speaker 02

  I mean, yeah. So what we saw the past couple of winters is this really interesting phenomenon where we had RSV peak and then flu took over and then COVID took over. They never really peaked at the same time, which really peaked a lot of our interest as epidemiologists to understand if there's like a competing demand here. On a biological level, it kind of makes sense, right? If your body is fighting flu, your immune system is already heightened and maybe preventing even more COVID transmission than before. But again, these are all just educated guesses right now and we'll see how this all plays out.

• 7:15Flora Lichtman?

  Let's go deep on norovirus, not a sentence I ever wanted to say. My family had it. Everyone I know has had it this year. It's this really nasty stomach bug. It's also been circulating at higher levels this year. Is that right?

• 7:29Speaker 02

  That is right. I mean, we just can't catch a break this winter. We've had incredible levels of norovirus, which is like you said, it's nausea, it's diarrhea. It's just not something you want to have. It's also very highly contagious. So if it hits a household, for example, typically that household all gets sick. And I think another question is why, right? A lot of people are wondering why we're having a bad norovirus season. And typically when we have a bad norovirus season, it means that norovirus mutated a bit to escape our immunity, just like flu and COVID can do that. We haven't had the genetic testing, not that I'm aware of, to know for sure that's what's happened,

• 8:14Speaker 02

  but that, that would be my guess what's driving this. Now, norovirus trends, looks like it has peaked. It's still above average levels right now, but it, it looks like it's on the way down. And I think all of us won't be complaining about that.

• 8:33Flora Lichtman?

  After the break, how living through a public health emergency has made us think differently about winter bugs.

• 8:40Speaker 02

  One silver lining, at least from this epidemiologist of the pandemic, is that people are paying more attention to, to viruses.

• 8:53Speaker 00

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• 10:36Flora Lichtman?

  Here's the question I want an answer to. Is it a coincidence that we are having this terrible year for norovirus? We're having this walking pneumonia surge. Flu is higher than it has been in decades. Is it a coincidence that this is all happening at the same time? Or is there-- do they interplay in some way?

• 10:54Speaker 02

  Yeah, I mean, one thing that I've seen rumbling on social media is questioning whether the COVID pandemic, COVID infections are weakening our immune systems. And we just have not seen the data to support that at a large population level. That may be happening among immunocompromised, for example, but that doesn't seem to be driving it. Another really interesting thing was behavior. And I think one silver lining, at least from this epidemiologist of the pandemic, is that people are paying more attention to viruses. And I think that they now realize there are things we can do to stop flu transmission

• 11:35Speaker 02

  that can prevent norovirus. And so a lot of the headlines and talk, I think, is also a result of us going through a major public health emergency, and we have increased awareness and education around all of this.

• 11:50Flora Lichtman?

  That's fascinating. You know, it's interesting because I have seen on social media, friends be like, oh, this was our adventure with flu A. And I was like, I never remember people calling out the flu family that they had. You know what I mean? Like, there is, I do think that there's something to that.

• 12:06Speaker 02

  I was just gonna say, I think that I was looking back at CDC data over, just looking at the total number of tests performed for influenza. And I also think there's a change in the way we are approaching respiratory viruses overall. I would love to look at, you know, overall volume of testing, and if we're just testing more than we used to in the past. So that comment about flu A, you know, many of the kind of rapid tests that people would do if they even got tested for flu in the past, would not have perhaps even told them which version of flu they had. But now people are getting much more testing. Some of that is indicated, and some of it is just not really necessary from a clinical perspective to know which particular virus one might have.

• 12:51Flora Lichtman?

  While we're on testing, Erica,

• 12:55Speaker 03

  Yeah.

• 12:55Flora Lichtman?

  You know, no viral conversation today is complete without talking about H5N1 bird flu. Is your hospital testing people for bird flu?

• 13:03Speaker 03

  So we are not testing broadly for bird flu. And in fact, I'm not aware of any facility that's doing that. Maybe I'll go through it piece by piece. So so far, about 70 cases in humans in the US. All almost all of those have had some notable exposure to animals where we know bird flu has been circulating. But there hasn't been documented person to person transmission. And at this point, that exposure history is really key in terms of risk factors. In terms of available testing, my own view is the focus of the testing really should be in individuals who have a relevant exposure history. And what's really challenging, I think, for most healthcare facilities is how do you elicit that exposure history

• 13:46Speaker 03

  in someone presenting to your facility in a in a way that's timely? And then you can figure out how to get the testing done. There are some of the tests that we have available at the hospital that will get down to the flu subtype. And they will say, in an example, if someone were to present and who actually had H5, it would be not typeable. And that would be a signal to dig further for that patient. But I think the vast majority of testing that's being done out there is not going to differentiate between strain types. So you really have to be attuned to that exposure history right now and then work with your local public health to sort out next steps in terms of additional testing and confirmation.

• 14:25Flora Lichtman?

  When we think ahead to the future, I mean, do you think this is something that we need to be working on? Creating more accessible tests for bird flu specifically?

• 14:35Speaker 03

  I think testing is so key. And I'm hoping that we'll start investing at this point in testing that is actually available and that can be put into the regular clinical workflows. So while there are commercial labs out there where you could send out a test too, or you could go to your public health lab and they could do the testing, that really does not work for the way healthcare is delivered and the timeliness in which we need these sorts of results. So right now, while it's really limited in specific risk populations, we need to be leaning forward and thinking about how do we get assays at the bedside or in the healthcare facility so that should we see more activity? Or should we need to make those sorts of decisions

• 15:20Speaker 03

  that we have the tools available to us? I can share that in in our facility, there is a research team that developed a research-only H5 assay, and they've been running it over the course of last summer, testing thousands of discarded samples, looking for H5, and then intermittently since that time. And at least in our area, which makes a lot of sense if you look at the national data on H5 detections in wastewater and then the cases, there really hasn't been much H5 around. But it's very geographical. And so in certain parts of the country, if you were asking someone in my position, they may have a different answer because they are dealing with their local epidemiology.

• 16:01Flora Lichtman?

  Caitlin, what are you looking for in terms of bird flu? What are you monitoring?

• 16:06Speaker 02

  I mean, we don't have a perfect data system in epidemiology, so we have to triangulate all sorts of data sources, one being wastewater. So our wastewater systems are able to test for H5N1. And this is one way we know, for example, that this huge flu wave we're seeing, you know, seasonal flu wave we're seeing right now is not due to H5N1 because the wastewater system isn't lighting up across the nation. The other thing we are very dependent on is, like Erica was saying, testing in hospitals as well as syndromic surveillance, which is basically people coming to the emergency department all across the United States

• 16:49Speaker 02

  and trying to find patterns of, for example, red eye and flu. And so we're trying to piece this puzzle as much together. But I will say, a lot of epidemiologists, including myself, are very frustrated because it does seem like we are flying blind. And if we were to start seeing human-to-human transmission, our systems are certainly not fast enough to stop it in its tracks.

• 17:15Flora Lichtman?

  You're flying blind because of current changes in availability to of data on CDC websites, or why?

• 17:24Speaker 02

  There's a couple of reasons. One is that there is a significant distrust in government among the highest risk. And the highest risk right now are farm operators as well as farm workers. And these are majority undocumented workers. They are majority agriculture, and they don't trust CDC coming in and asking them to test once they're exposed to sick animals, for example. So there's a really big challenge with that. And you're right, there's also been very little communication in the past four weeks

• 18:05Speaker 02

  from this new administration on what is going along with H5N1, and very little transparency. And so us in epidemiology always think that there could be more testing. And of course, it is a balance between resources and willingness and feasibility.

• 18:23Flora Lichtman?

  Erica, any final tips for staying healthy for the rest of flu season?

• 18:28Speaker 03

  Well, if you haven't gotten vaccinated, you should absolutely get vaccinated. There's still time. I think the other part that some people may not realize is that in terms of treatment for the flu, there is a treatment available. The treatment works best when it's given early in the infection. If you're an individual who may be at risk for severe complications of the flu, so if you have asthma or other underlying lung disease, diabetes, heart disease, if you think you have flu, reach out to your provider. They can even treat you without a positive test. And I think that sometimes people don't realize that for influenza, especially this time of year with this amount of flu circulating, that we don't want testing to be a barrier.

• 19:11Speaker 03

  And we can certainly prescribe and make a clinical diagnosis that you have flu and prescribe the right treatment.

• 19:17Flora Lichtman?

  I want to thank you both for taking the time to break this down for us.

• 19:20Speaker 02

  Yeah, thanks for having me.

• 19:22Speaker 03

  Yeah, thanks for having me. It was fun.

• 19:24Flora Lichtman?

  Dr. Caitlin Jetelina, epidemiologist and author of the newsletter, Your Local Epidemiologist. She's based in San Diego, California. And Dr. Erica Shinoy, Chief of Infection Control at Mass. General Brigham, based in Boston, Massachusetts.

• 19:40Flora Lichtman?

  And that is about all we have time for. Lots of folks helped make this show happen, including...

• 19:46Speaker 00

  Dee Petersman. Phyllis Samars.

• 19:48Flora Lichtman?

  Emma Gomez. Jackie Hirschfeld. I'm Flora Lichtman. Thanks for listening.