According to data released Monday by the U.S. Centers for Disease Control and prevention, during the current flu season in the U.S, the number of cases hospitalized with common influenza symptoms has reached the highest level in the country since the 1997-1998 influenza season.
“This is the worst year in at least 20 years,” said Caitlin Rivers, an epidemiologist and senior fellow at the Center for Health Security at Johns Hopkins University. “We’re seeing very severe outbreaks across much of the country,” she said, against the backdrop of a severe flu season in the US last year, it is surprising that this year’s flu season is intensifying, as two severe flu seasons do not normally occur in a row.
In the last week of 2025, about 8.2 percent of visits to health facilities nationwide were for flu-like symptoms, according to the data. That’s up from 6.7 percent in the last flu season. Nearly all states have high or very high levels of flu activity.
The U.S. Centers for Disease Control and prevention estimates that at least 11 million people have contracted flu in the United States this season, 120,000 have been hospitalized and 5,000 have died, including children.
Adult vaccinations have declined in recent years, from nearly 61 million in 2019-20 to about 48 million this year, according to CDC data. Childhood influenza vaccination rates have also been declining, from a high of 53% in the 2019-2020 influenza season to 42% in the same period of the current influenza season.
People who have not yet been vaccinated should be vaccinated as soon as possible to avoid the final stages of the flu season, experts say. However, rivers believes that the emergence of a new strain of the virus“Sub-branch K” is the real reason for this year’s increased level of flu activity. She said the variant strain could bypass existing immune defences and that previously selected flu vaccines might offer only partial protection.