Flu FAQ: Is the flu worse this year? Here’s what you need to know

U.K. health officials analyzed preliminary flu data and predicted that subclade K may spread more easily than other versions. The researchers estimated that the reproduction number of subclade K is 1.4, meaning that each infected person spreads the virus to 1.4 other people on average. Typically, the reproduction number of the flu is closer to 1.2.

While there will be more flu cases this year, so far, there is no evidence that this new flu version will cause more severe cases, hospitalizations or deaths. Health officials have already recorded many more cases this year than at the same time last year, about 4.5 million cases compared to 1.9 million in 2024. But of those nearly two million cases last year, 1.2% were hospitalized and 0.05% died from their infections. So far in 2025, the rate of hospitalization is 1.09% and the mortality rate is 0.04%.

The CDC has not yet commented on the effectiveness of this year’s flu vaccine in the U.S. But U.K. health officials previously estimated that their vaccine, which is different from the one used in the U.S., reduced hospitalizations by about 70-75% in kids and by about 30-40% in adults.