How A Mutation Made This Year’s Flu Season So Bad

A flu variant called subclade K emerged too late to be fully covered by this year's vaccine. But the flu shot can still help protect you.

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

• 0:03Flora Lichtman?

  Hey, it's Flora Lichtman and you're listening to Science Friday.

• 0:07Speaker 01

  The super flu is here and it's wreaking havoc across the nation.

• 0:11Speaker 02

  Health officials confirm a new strain of the flu is spreading. It's very contagious and it lasts longer.

• 0:17Speaker 03

  Here in the United States, the number of children hospitalized for the flu hitting the highest weekly rate in more than 15 years. That's not good.

• 0:24Flora Lichtman?

  No, it is not good. The so-called super flu has sickened more than 19 million people in the U.S. so far this season. And the flu shot hasn't offered that much protection. So what is going on with this super flu storm? Here to cough up some answers is Dr. Jennifer Duchan, pediatric infectious disease specialist at Mount Sinai Hospital in New York. Welcome, Jen.

• 0:47Speaker 04

  Hi, thank you for having me.

• 0:49Flora Lichtman?

  Let's talk branding. Is it a super flu? Does that actually mean anything?

• 0:54Speaker 04

  So that is a little bit sensational. Certainly, we've seen a lot of cases of flu and people are sick with it. But in terms of that terminology, we can kind of break it down into case numbers and virulence. So is it a super flu in terms of virulence? So is it causing people to have more severe disease? The jury's still kind of out on that. In terms of case numbers, absolutely. We're seeing a lot more cases of the flu this year.

• 1:29Flora Lichtman?

  You know, I know people who got vaccinated for flu still got really sick. Did the vaccine miss the mark? What happened there?

• 1:37Speaker 04

  Yeah, so that's really interesting. And that's really one of the reasons why I love my profession, because, you know, there are always surprises. So the flu vaccine is made in advance of the flu season, using a combination of microbiologic and global surveillance data, as well as some modeling. Last year's strains are sort of modeled to see how they're going to change. And the yearly flu vaccine is targeted to that strategy.

• 2:10Flora Lichtman?

  And last year in the US or sort of southern hemisphere strains that might come our way?

• 2:16Speaker 04

  Global, global. We have global surveillance data. The WHO, in conjunction with many different nations, actually has biologic data from strains that are collected through various laboratories. And so we're able to do some, some pretty sophisticated modeling in terms of how global flu strains are going to mutate or change for the next season. So, you know, what generally happens, so they make the flu vaccine and what we, what we usually have first is the southern hemisphere data. That's because their summer is our winter, our winter is their summer. So as flu is generally a winter-spring virus, the southern hemisphere sees it first.

• 3:01Speaker 04

  So everyone, as typical, got the flu vaccine as they, as they normally would in the southern hemisphere. And what seemed to happen is that one of the flu A strains in H3N2 developed some mutations on one of the antigens. What we noticed was this H3N2 strain called subclade K had a couple of different mutations. And so the vaccine that we had developed wasn't, didn't really cover this very well.

• 3:40Flora Lichtman?

  And then it's sort of too late, right? Because the vaccine's already been developed.

• 3:44Speaker 04

  Right, exactly. So, you know, I can tell you that because these are mutations and not dramatic shifts, the flu vaccine does still protect against major complications of the flu. That includes severe pneumonia, hospitalizations. So, you know, we're still recommending that people get the flu vaccine. But yeah, I mean, flu is tricky. And it's kind of interesting. There are some reports now that are, that are showing that the southern hemisphere is actually having a second peak of flu with this particular, what we call subclade.

• 4:19Flora Lichtman?

  This K, this super K, as it's been dubbed in the media. I mean, is the K subclade, is this like a new twig on the flu family tree?

• 4:31Speaker 04

  Yeah, that's kind of actually a good way to describe it. So it's within the strain of H3N2. But what happened is a couple of the proteins basically mutated. So they mutated by surprise, which again is a feature of the flu. We know it mutates every year and often we're surprised. For example, we saw an entirely new strain in 2009, the H1N1. This is a little bit different than that. So this isn't an entirely new strain. This is basically just what we call antigenic drift. Some of those antigens have mutated and drifted.

• 5:08Flora Lichtman?

  You know, you mentioned that the flu shot can still be protective against sort of the most severe disease. Can we get nerdy for a second? How does that work? If it's not a match for K, you know, this K subclade, how is it offering protection?

• 5:22Speaker 04

  Yeah, so those proteins aren't completely changed. So they don't mutate such that the flu vaccine doesn't recognize those and stimulate your immune system to recognize those proteins completely. It's more of a partial protection. And every year, the CDC studies what happened, usually at the end of the flu season and reports that. And the H3N2 strain is usually the one that's the trickiest. And this again is the one that had those antigenic drifts.

• 5:56Flora Lichtman?

  Wait, why is this, why is, why is H3N2 the problem child?

• 6:02Speaker 04

  You know, probably because again, it seems to have the most ability to mutate and change. That's not a hard and fast rule, but that's the one that we seem to grapple with the most. So there are multiple flu strains that are put in the flu vaccine. Since the H1N1 came about, we've been including that. There's the H3 strain and there are also some flu B strains. And that's another reason why it's really important to get vaccinated. Because right now, about 90% of circulating flu strains are this H3N2 subclade K. But that may change throughout the season. Last year, we saw a sort of a late peak of influenza B.

• 6:45Speaker 04

  And that's pretty well covered by the flu vaccine.

• 6:49Flora Lichtman?

  Yeah. I mean, is there any hope for solving this mismatch problem? Like a universal flu vaccine or a different way of doing things?

• 6:59Speaker 04

  There's always hope. Although usually, I have to say, I'm sort of Debbie Downer. Like, I'm the person that you don't want to have at your dinner party.

• 7:07Flora Lichtman?

  I love Debbie Downers. You're always invited to my dinner party. We can Debbie Down together.

• 7:13Speaker 04

  We can sit in a corner and talk about flu. So, yes, unfortunately, some of that research has been put on the back burner.

• 7:24Flora Lichtman?

  You don't say.

• 7:26Speaker 04

  Interesting, right? So, there is a global effort to develop what's called a universal flu vaccine. Some of those efforts involve mRNA technology. Some of them don't, but that's been put on the back burner for the time being, especially in the US where a lot of our vaccine research has unfortunately been affected by recent changes in the CDC architecture.

• 7:55Flora Lichtman?

  Well, speaking of that, I mean, earlier this year, the CDC changed recommendations for childhood vaccines and stopped universally recommending that kids get the flu vaccine. What are your thoughts on that as a pediatric infectious disease specialist?

• 8:10Speaker 04

  Yeah. So, that's an unmitigated disaster, huh? So, we know that even by the CDC's own data, that children have the highest hospitalization rate next to the elderly. So, making those recommendations is really grossly irresponsible. And I'm not the only one that feels that way. I think that infectious disease physicians, general pediatricians, anyone who works with children is just really disappointed by those recommendations.

• 8:45Flora Lichtman?

  Are fewer people getting the flu shot this year? And is that a factor in why we've seen so many cases?

• 8:52Speaker 04

  It's definitely a contributing factor. And yes, the flu vaccine is one of those vaccines that tends to have poor uptake anyway. So about 43% of eligible children this season thus far have been immunized. Of course, that's terrible. You know, there are a lot of reasons for that. It's annually. If people are going to skip something, they're going to skip something that, you know, you have to remember to get every year. I really give a lot of credit to the general pediatricians that I work with.

• 9:32Speaker 04

  They're on the ground and trying to do their best in making sure that everyone comes in for their visit. But it can be, it can be challenging. So, you know, also the elephant in the room, or not such an elephant in the room, is that certainly since COVID, vaccine uptake, especially for flu, has been diminished.

• 9:58Flora Lichtman?

  Yeah, yeah.

• 10:00Speaker 04

  And I sort of, I mean, a lot of this renders me speechless, unfortunately. I'm, I'm sorry that we, that we got here. And I'm really hoping that it doesn't take a long time to reverse course, but I don't know that that's necessarily the case.

• 10:16Flora Lichtman?

  Wow, it renders you speechless.

• 10:18Speaker 04

  Yes, it really does.

• 10:20Flora Lichtman?

  Say more about that.

• 10:23Speaker 04

  Well, I'm speechless.

• 10:27Flora Lichtman?

  Touche.

• 10:28Speaker 04

  Touche.

• 10:29Flora Lichtman?

  Okay, I want to wrap up with a different kind of question.

• 10:31Speaker 04

  Yeah.

• 10:32Flora Lichtman?

  You're a doctor. When you go down with the flu, what's your remedy? Rewatching Mad Men, ginger shots? Like, what do you do?

• 10:45Speaker 04

  I personally prefer to kick everybody out of the room, close the door, not speak to anybody. That doesn't work. Usually what I end up doing is working from home. But we do, by the way, have antivirals that can help shorten the duration of flu, if you get it, and you start to take those medications in a timely manner, can help prevent sort of the really severe consequences of the flu, such as pneumonia, hospitalization, dehydration. So I've already, I already have my prescription in lock for one of those particular medications. We kind of forget that one of the reasons to test

• 11:28Speaker 04

  is to be able to use one of those treatments, one of those therapies.

• 11:33Flora Lichtman?

  Okay, so take some medicine and kick everybody else out of the room.

• 11:37Speaker 04

  Yeah, yeah. And one of the TV stations where I live has like 24/7 Law and Order Marathon. So that's what I like to do. My husband prefers Storage Wars, but we have two TVs, so it's fine.

• 11:52Flora Lichtman?

  Dr. Jennifer Duchan is a pediatric infectious disease specialist at Mount Sinai Hospital in New York. Jen, thanks for joining us.

• 11:58Speaker 04

  Thank you.

• 12:00Flora Lichtman?

  This episode was produced by Kathleen Davis. And if you have a question, or a comment, or something you want us to look into, please give us a ring, 877-4-CY-FRI, 877-4-CY-FRI. The listener line is always open. See you tomorrow. I'm Flora Lichtman.