01/07/2026
đˇInfluenza-like illness rates (cough, fever, sore throat) are very high and rising exponentially. It's the highest this metric has been in 6 years.
Why is this flu season so intense?
1. One flu strainâcalled influenza A (H3N2)âmutated over the summer as it circulated in the Southern Hemisphere. While this is normal, the changes it made this year are more substantial than normal. The timing of the mutation was also just plain bad luck. It occurred after this year's flu vaccine formula was finalized in February. That means this yearâs vaccines likely recognize part, but not all, of the updated virus.
2. Vaccination rates, especially among children, continue to decline substantially. Last year was the deadliest non-pandemic flu season for U.S. children on record. It also happened to have one of the lowest flu vaccination rates. This season, the vaccination rate is even lower.
**Vaccination still matters. Even a mismatched flu vaccine still provides some protection against severe illness. This is because the vaccines still train the immune system to recognize viral components that havenât changed. Also, there is more than one flu strain circulating (not just H3N2). Preliminary data from the U.K. show that flu vaccination reduces hospitalization by 70â75% in kids and 30â40% in older adults.