Flu season arrived early this year, and one virus strain is behind almost every case doctors are seeing.
Quick Take
- The Centers for Disease Control and Prevention (CDC) says flu activity started rising in late August, weeks earlier than normal.
- Nearly 99% of subtyped flu samples in late October were A(H1N1)pdm09, the same H1N1 lineage that emerged back in 2009.
- Hospitalization rates this October are running far above last year’s numbers for the same week.
- CDC says national flu activity is still officially “low,” even though it is rising faster than usual.
An Early Start That Caught Health Officials’ Attention
The CDC’s weekly flu tracking report, called FluView, flagged something unusual in early October. Flu activity had been climbing steadily since late August, and that is much earlier than the typical fall ramp-up. By the week ending October 3, the agency said activity was “currently higher than typically observed at this time of year”. Three weeks later, the pattern had not slowed down.
By the week ending October 24, the CDC reported that multiple warning signs were all pointing the same direction. More people were testing positive for flu. More patients were showing up at doctors’ offices and emergency rooms with flu-like symptoms. And more people were landing in the hospital with confirmed flu, all earlier than usual for the season.
One Strain Is Driving Almost Every Case
The lab numbers tell a striking story. In the week ending October 3, 125 of 127 subtyped influenza A samples, or 98.4%, came back as A(H1N1)pdm09. Two weeks later, that number climbed to 99.2%. By October 24, it held steady at 98.9%, with the CDC noting this single strain made up nearly 83% of all influenza A viruses reported since late May. That is about as close to a single dominant strain as flu surveillance ever shows.
This is not a brand-new virus. A(H1N1)pdm09 is the same influenza A subtype that caused the 2009 swine flu pandemic and has circulated as a normal seasonal strain ever since. CDC’s surveillance reports describe it as the familiar 2009 lineage, not a newly emerged pandemic threat. Local reporting has raised the question of whether a mutated version is behind this year’s early surge, but the CDC’s own lab data classifies the circulating virus under that same established subtype.
Hospitalizations Already Outpacing Last Year
Numbers reported elsewhere show the scale of the early jump. One tracking comparison found 2.1 flu hospitalizations per 100,000 people during a recent week, versus just 0.2 during the same week in 2025. That is roughly a tenfold increase year over year. Independent reporting backs up the trend, noting infections were climbing in 44 states by late October, with H1N1 responsible for the vast majority of confirmed cases nationwide.
Activity is not spread evenly across the country. Parts of the West have seen especially sharp increases, while states like Louisiana and Hawaii have reported only moderate flu activity so far. That regional patchwork matters. National averages can mask very different realities depending on where you live, and a county seeing a big spike does not mean every state is experiencing the same surge.
Why Early Does Not Automatically Mean Severe
History offers a useful guide here. The 2009-2010 pandemic season also started unusually early, with H1N1 dominant, and activity actually peaked in October before dropping off fast by January. The 2022-2023 season likewise began rising earlier than normal and ended up moderately severe, not catastrophic. CDC itself cautions that an early increase does not guarantee a bigger or worse peak later in the season. Timing alone is not destiny.
CDC's latest FluView (week ending Oct 24) confirms the first pediatric flu death of the 2026-27 season, linked to influenza A(H1N1), with the death occurring the week ending Oct 10. Lab-confirmed flu hospital admissions reached about 6,100 for the week, and children 0-4 had the… pic.twitter.com/9QPAiaVgfK
— Eric Doherty (@EDohertyGlobal) November 3, 2026
What is clear is that flu arrived ahead of schedule this year, with one strain dominating lab results across the country. CDC still classifies overall national activity as low, even as individual indicators climb faster than usual. Health officials continue recommending the annual flu vaccine as the most reliable tool available, regardless of which strain ends up circulating most this winter. The next several weeks of surveillance data will show whether this early rise turns into a rough season or fades quickly, the way it has in past H1N1-heavy years.
Sources:
menshealth.com, cdc.gov, freep.com
