インフルエンザ変異株「サブクレードK」はインフルエンザシーズンを悪化させるか？

インフルエンザ変異株「サブクレードK」はインフルエンザシーズンを悪化させるか？

Flu experts are warning that the 2025 2026 flu season could be a rough one. That’s largely because of subclaid K, a flu variant that has emerged this year. So what is subclaid K? Is this year’s flu vaccine any match for it? And what about it is making experts nervous about the upcoming flu season? All that and more in this week’s status report. [Music] Last year was a very bad flu season. It was the worst since the 2020 2021 season when CO measures like social distancing and masking are credited for bringing flu transmission down to virtually zero. In fact, every year since 2021 has had increasing amounts of flu hospitalizations. There are two main types of flu A viruses, H1N1 and H3N2. Of the two, H3N2 is considered to be more dangerous, and it’s H3N2 that is mutated into the new subclaid K variant. To understand why this is worrying, here’s a refresher on how flu vaccines work. Every year, the World Health Organization identifies the flu strains it believes are more likely to spread in the upcoming season. Fragments from those virus strains are used by vaccine manufacturers to create that year’s vaccine. Those fragments trigger the immune system to create antibodies which prepare the body to fight off those strains if they are encountered. But the vaccine can’t prepare the immune system for every type of flu. If a different flu is encountered or if the original strains have mutated, the antibodies may not recognize them, making it more likely that the virus will trigger an infection. In this past summer, the original strain did mutate with subclate K. And by then, it was too late for the vaccine manufacturers to use fragments from subclate K in this year’s flu shots. stats. Infectious diseases correspondent Helen Branswell recently spoke to several flu experts about the upcoming flu season. Why it might come early this year, why this year’s shot may not be as robust, and why despite this, it is still vital to get a flu shot. I’ll talk with Helen about all that and more in just a sec. But first, if you’re enjoying this video, uh please like and subscribe. Every week, Status Report will keep you up to date with all the most important news in health and medicine. It’s a little click, but it helps us out a lot. Okay, let’s chat with Helen. Hey Helen, thanks so much. Nice to be here. So, the CDC just released a new flu report. Um, did it say anything about how prevalent subcla K is right now? Yeah, it did. Uh, so they just posted on Monday the flu data for the week ending November 22nd, the week just before Thanksgiving. And um it shows that at present the vast majority of viruses that are circulating are influenza A. As you mentioned earlier in your intro, uh flu A has comes in two types H1N1 and H3N2. Um H3N2 is the predominant virus so far this year. It makes up about 80% of the viruses that have been tested so far. And of the H3N2 viruses that have been tested so far, subclaid K viruses make up about 57%. So it is definitely out there in significant numbers. So this year’s flu vaccine might not be a great match for subcl. Um but flu experts you spoke to still recommend getting vaccinated. Um why is that? Well, there are a few reasons. For one thing, H3N2 is not the only virus and even though it’s the predominant virus right now, um that may change over the season that that you know that is seen quite commonly at the beginning of the season. Sometimes you have a lot of H um influenza A activity and then late in the season you can have a surge of influenza B activity. So just because the vaccine may not be super well suited to H3N2 right now doesn’t mean it wouldn’t offer protection against um H1N1 or influenza B viruses. And you know as I mentioned a minute ago um subplate K makes up about uh 57% of the H3N2 viruses that are circulating right now. But that means 43% of the viruses the H3 and2 viruses are not subclave K. In addition um even if you know somebody’s vaccinated and encounters a subclaid K virus it doesn’t mean that the vaccine would offer them no protection at all. uh scientists in the United Kingdom where there’s been a very early start to their flu season largely because of uh H3N2 subclave K did a study looking at people who’ve been recently vaccinated and they found that there was good protection against getting sick enough to require hospital care from the vaccine. Is there any indication that subclaid K is causing more severe illness? Uh not at present. No. Um I checked with people uh flu experts I know in Hong Kong which had a very early flu season largely driven by subplate K. And in Australia which had a long extension of their flu season because of the emergence of some clay K there were in both cases there were a lot of cases in Hong Kong there were even a lot of hospitalizations but it wasn’t there was no indication that there was increased severity from the from the infection and and some other countries you mentioned are having an early flu season Is that going to be the case here in the US? Well, so far the data don’t show a strikingly early season. Um, you know, the last few years, right about now has been about the time that the flu season has started to kick into gear. And that’s not uncommon when you think about uh the amount of travel and intergenerational mingling that happens during the um Thanksgiving. It’s a perfect opportunity for uh flu to take off. That said, sometimes flu season doesn’t take off until sort of January, but it’s really not uncommon for activity to start to pick up in late November, early December. And if you look at this season’s um sort of epic curve so far, it’s very similar to the last few years. So many uh folks that study uh influenza say that trying to predict flu season is is a bit of a fool’s errand. Why is that? Because flu will always do the thing you don’t think it’s going to do. I mean there are some givens. You know flu will generally come back. But flu is just a very unpredictable virus. You can see it in flu studies. people set up a study to try to see how the virus does and it’s a one season study and the virus just doesn’t cooperate. You know, uh a recent example there was data published by uh Fizer in the New England Journal of Medicine recently. They did a a phase three trial trying to see how well their um modified mRNA flu vaccine worked. And in that season there was almost no flu B. So they couldn’t give any kind of an estimate of how well it worked against the vaccine worked against flu B. That’s really common with flu. You just you just never know exactly what it’s going to do. And uh lastly and most importantly um do you think Sydney Crosby and Con McDavid are going to take it to team USA uh this year in Milan? Uh yes. All right. What did you expect from a Canadian? Helen, thanks so much. I appreciate the time. It’s always good talking. Okay, thanks Helen. It’s always great to chat and I’m looking forward to being bitter rivals in a couple months from now and I’m excited for next week’s video. Status report is taking the show on the road for Ash 2025. I’ll be at the American Society of Hematy’s 66th annual meeting in Exposition to learn what’s new with blood. And if you’re going to be in Orlando for Blood of Palooa, come say hi at our Stata Dash event Friday night from 6:00 to 9:00 p.m. Otherwise, I hope to see you here next week. Same stat time, same stat channel. [Music]

Every year, vaccine manufacturers rely on guidance from the World Health Organization to know what influenza strain to target with their flu shots. But sometimes the strains that end up circulating in peak flu season do not match the strains used for making the vaccines.

Sometimes this happens because a different flu strain ends up becoming dominant, or because the strain identified for the vaccines has mutated. This year, it’s the latter — a variant of H3N2 flu virus called subclade K has emerged.

In this week’s STATus Report, host Alex Hogan chats with STAT infectious diseases correspondent Helen Branswell about how prevalent subclade K is right now, if it causes more severe illness than other strains of flu, and why flu experts still recommend getting your flu shot despite the mismatch.

0:00 Intro
1:01 How flu vaccines work
2:13 How prevalent is subclade K?
3:15 Do flu experts recommend vaccination?
5:09 Does subclade K cause more serious illness?
5:54 Will flu season come early this year?
6:49 Why is flu so hard to predict?
7:59 Helen’s Olympic Hockey prediction
8:20 Outro/STAT@ASH 2025