What to Know About the New 'Subclade K' Flu Variant

Flu season has come early in the U.K. Cases began to tick up in October, more than a month ahead of when epidemiologists generally expect the season to start. Driving the surge is a new variant, and while flu viruses are always evolving, this one has racked up an impressive number of mutations relatively quickly. “This one has evolved a bit more rapidly, with more changes than we normally see,” says Jamie Bernal Lopez, a consultant epidemiologist at the U.K. Health Security Agency (UKHSA). What is subclade K? The variant is known as influenza A subtype H3N2 subclade K–sometimes called “subclade K” for short—and it has been detected in Japan as well, where public health authorities declared a flu epidemic last month. The mutations mean the variant is a bit different from the viral material included in this year’s updated vaccines. At the end of October, Canadian scientists warned that the mutations warranted close observation, including regular sequencing of virus DNA and checks to see whether current vaccines are working.   On Nov. 12, Bernal Lopez and his colleagues at the UKHSA released preliminary results from the U.K. suggesting that so far, vaccination is still providing significant protection against hospitalization and severe illness.  However, they note that the level of protection is closer to what they usually expect to see at the end of a flu season, when vaccine effectiveness has waned a bit and the mismatch between the vaccine and the virus has increased.  Does that mean the later stages of this season will be especially bad?  “Flu is notoriously unpredictable, so it’s very difficult for us to say what’s going to happen,” says Bernal Lopez. It’s possible “that we’ve got an earlier season and that it finishes earlier, but I think the fact that we have seen earlier activity—and the fact that we have this concerning subclade—increases the chance that we’re going to see a more intensive flu season than we normally do.” Dr. Antonia Ho, professor and consultant in infectious diseases at the University of Glasgow, adds that earlier flu seasons often mean more people get the flu. What’s more, seasons driven by H3N2 flus, like this one, also tend to hit the elderly quite hard, she says. Is subclade K in the U.S.?  During the government shutdown, the flu-tracking website maintained by the U.S. Centers for Disease Control and Prevention has not been updated. As of Nov. 13, the last available numbers are from the last week of September, when flu activity was low. However, the New York State Department of Health’s flu surveillance report for the week ending Nov. 1 showed an increase in laboratory-confirmed flu cases, up 49% from the previous week. Flu hospitalizations were up 71%, with levels matching approximately where they were last year at this point in the flu season. The data do not include detailed subtyping, so they can’t reveal whether the new variant has arrived. How to protect yourself from the flu  The best protection against flu, Bernal Lopez stresses, is to get vaccinated. Each year influenza kills thousands of people, and it is particularly dangerous to the young and the elderly. “Children are at increased risk of severe disease with flu, so it’s very important that they get vaccinated themselves. But it also provides protection [for] their relatives, and in particular, any vulnerable relatives or elderly relatives that might be exposed,” says Bernal Lopez. Even with this new variant’s mutations, the vaccine is still an important tool against the disease. It can take up to two weeks for the flu vaccine to take effect, so the sooner you get one, the better.  “It remains our best tool to protect each other,” says Ho.