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December 16, 2025<\/p>\n
3 min read<\/p>\n
Add Us On Google<\/span>Add SciAm<\/span><\/span><\/p>\n New Flu Variant May Be Triggering Spike in Severe Disease<\/p>\n A novel influenza variant called subclade K appears to be driving an uptick in cases and hospitalizations throughout the U.S. and other countries<\/p>\n By Tanya Lewis edited by Claire Cameron<\/span><\/p>\n Deb Cohn-Orbach\/UCG\/Universal Images Group via Getty Images<\/p>\n There\u2019s a new flu variant in town, and it ain\u2019t pretty.<\/p>\n A mutated form of the influenza A strain H3N2 known as subclade K is causing a severe flu season in multiple countries across the world, including the U.K., Canada and Japan, and propelled a bad flu season in Australia. Now U.S. officials say it is driving up cases and hospitalizations here, too.<\/p>\n \u201cRight now we\u2019re seeing clade K everywhere we are seeing influenza\u201d in the U.S., said Andrew Pekosz, a professor and vice chair of the department of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, in a press conference today.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n Worryingly, the mutations in the subclade K variant may make this year\u2019s flu vaccine less effective. But experts say the shot, which was developed months before the new variant was identified, should still provide some protection against severe disease and death. The mutations \u201cmay allow it to evade some but not all of the influenza-vaccine-induced protection,\u201d Pekosz explained.<\/p>\n \u201cWe\u2019re still in the middle of trying to figure out whether it\u2019s producing worse illness or whether what we\u2019re seeing is a large number of cases that are increasing, and then there\u2019s a correspondingly similar increase in terms of the severe illness,\u201d he said.<\/p>\n Flu viruses are constantly evolving, but often these changes are relatively minor\u2014a process known as antigenic drift. But sometimes a virus undergoes an evolutionary leap, or antigenic shift\u2014and that can trigger a pandemic. Subclade K, while a significant change, is still considered to have undergone antigenic drift.<\/p>\n \u201cThe emergence of the new H3N2 influenza [subclade K] is concerning, as this variant emerged following development of the current-year influenza vaccine,\u201d says physician Robert Hopkins, medical director of the National Foundation for Infectious Diseases. \u201cBut influenza is difficult to predict.\u201d<\/p>\n The most recent update from the U.S. Centers for Disease Control and Prevention for the week ending on December 6 noted that flu infections are picking up across the country. Right now just four states are seeing high or very high influenzalike illness activity, but it\u2019s still early in the flu season, which, in the U.S., typically starts in October and may not peak until February. Recent data indicates that 89 percent of flu viruses sampled since September 28 belonged to subclade K.<\/p>\n Cumulative hospitalization rates, at nearly seven cases per 100,000, are currently in line with previous years. But that\u2019s starting to change in some places. Texas has seen an uptick in hospitalizations\u2014potentially driven by the new variant\u2014especially in those aged 65 and older.<\/p>\n The 2024\u20132025 flu season was one of the most severe in recent decades. While it\u2019s rare to have back-to-back bad flu seasons, it\u2019s not unheard of. And while this year\u2019s flu shot may not be a perfect match for subclade K, the vaccine should still provide protection\u2014even in those who are infected with the new variant, Hopkins says.<\/p>\n \u201cIt is not too late to get a flu shot,\u201d Pekosz said at the press conference.<\/p>\n Additional reporting by Lauren J. Young.<\/p>\n Editor\u2019s Note (12\/16\/25): This article was edited after posting to correct the number of states that are seeing high or very high influenzalike illness activity and to better clarify the descriptions of the subclass K variant and the U.S.\u2019s cumulative influenza hospitalization rates for the week ending on December 6.<\/p>\n If you enjoyed this article, I\u2019d like to ask for your support. Scientific American<\/span> has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.<\/p>\n I\u2019ve been a Scientific American<\/span> subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm <\/span>always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.<\/p>\n If you subscribe to Scientific American<\/span>, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.<\/p>\n In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.<\/p>\n There has never been a more important time for us to stand up and show why science matters. I hope you\u2019ll support us in that mission.<\/p>\n","protected":false},"excerpt":{"rendered":" December 16, 2025 3 min read Add Us On GoogleAdd SciAm New Flu Variant May Be Triggering Spike in Severe Disease A novel influenza variant called subclade K appears to be driving an uptick in cases and hospitalizations throughout the U.S. and other countries By Tanya Lewis edited by Claire Cameron Deb Cohn-Orbach\/UCG\/Universal Images Group<\/p>\n","protected":false},"author":1,"featured_media":37757,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[50],"tags":[4391,4255,7415,1320,20804,18482],"class_list":{"0":"post-37756","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-environment","8":"tag-disease","9":"tag-flu","10":"tag-severe","11":"tag-spike","12":"tag-triggering","13":"tag-variant"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/37756","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=37756"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/37756\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/37757"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=37756"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=37756"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=37756"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}On supporting science journalism<\/h2>\n
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