The 2024-25 flu season was significantly worse than average by one critical measure: it produced the highest number of pediatric flu deaths (280) reported since tracking began in 2004, second only to the 2009 H1N1 pandemic (288). Overall flu activity has since dropped to minimal levels across most of the U.S., but the season that just ended was notably harsh, particularly for children and older adults.
Whether you’re looking back at last winter or preparing for next fall, here’s what the data actually showed and what it means for you.
How the 2024-25 Season Compared to Past Years
The 2024-25 season was dominated by influenza A, which accounted for 94% of all positive flu tests in public health labs. Within that, the split was roughly even: 53% were H1N1 and 47% were H3N2. A small fraction (about 6%) were influenza B viruses, all from the Victoria lineage.
The clearest sign that this season was worse than usual comes from pediatric mortality data. The CDC reported 280 flu-related deaths in children, a rate of 3.8 deaths per million children. Before this season, the previous high (outside the 2009 pandemic) was 210 deaths during the 2023-24 season. For context, during the 2020-21 season, when pandemic precautions were still widespread, only one child died from flu. The upward trend over the past two seasons is striking.
Which Strains Drove the Severity
H3N2 seasons tend to be rougher than H1N1-dominant ones, especially for older adults. This season featured a near-even mix of both, which meant no age group was spared. H3N2 is particularly associated with higher hospitalization rates in people over 65, while H1N1 tends to hit younger adults and children harder. Having both circulating at high levels simultaneously created a wider impact across age groups than a typical season dominated by just one subtype.
Globally, H3N2 subclade K emerged as the dominant strain in several regions. In the Western Pacific, it represented 89% of sequenced viruses by late 2025, signaling that this particular variant spread efficiently and may continue circulating into the next season.
How Well the Vaccine Worked
Vaccine effectiveness was moderate, which is fairly typical for flu shots but still leaves room for a lot of illness to get through. Across multiple CDC tracking networks, the numbers looked like this:
- Children and teens: 59-63% effective at preventing outpatient visits and hospitalizations in the best-performing networks, though one network estimated as low as 32% for outpatient protection.
- Adults 18-64: 37-56% effective at preventing doctor visits, and 48-51% effective against hospitalization.
- Adults 65 and older: 51-57% effective against hospitalization in larger networks, but one smaller network estimated outpatient effectiveness as low as 18%, with wide uncertainty.
The inconsistency across tracking networks reflects real-world variability. Larger networks (like VISION, which draws from major health systems) generally showed higher effectiveness than smaller study sites. The takeaway: the vaccine reduced your risk meaningfully but was far from a guarantee, especially for older adults.
Antivirals Still Work
One piece of genuinely good news: none of the circulating flu strains showed resistance to available antiviral medications. The CDC tested 266 virus samples against three common antiviral drugs and found zero cases of reduced effectiveness. An additional 237 samples tested against a newer antiviral also showed no resistance. This means that if you get sick and start treatment early (within the first 48 hours of symptoms), antiviral medications remain a reliable option for shortening illness and reducing severity.
Where Things Stand Now
As of mid-April 2026, flu activity across the U.S. is minimal. The vast majority of states report the lowest activity level, with only a handful showing low or moderate levels. This is normal seasonal winding-down. Flu seasons in the U.S. typically peak between December and February, then fade through spring.
The more relevant question for most people is what’s coming next. The composition of the 2025-26 flu vaccine has already been selected based on which strains circulated most recently, including the H3N2 subclade K variant that dominated globally. How well that vaccine matches whatever actually circulates next winter remains the biggest unknown. Given that the past two seasons have each set or approached records for pediatric deaths, getting vaccinated early in the fall, particularly for children and older adults, carries more weight than it might have a few years ago.