By Harshit
WASHINGTON, DECEMBER 15 — 6 AM EDT
The U.S. flu season is now officially underway, according to federal health data, as a new influenza variant fuels an early and unusually intense rise in cases across multiple regions of the country. Health officials say post-Thanksgiving travel, indoor gatherings, and lagging vaccination rates are accelerating the spread, raising concerns about a difficult winter ahead.
For the week ending December 6, the proportion of outpatient doctor visits for flu-like illness — defined as fever accompanied by cough or sore throat — rose to 3.2%, according to the U.S. Centers for Disease Control and Prevention (CDC). That figure exceeds the national epidemic threshold of 3.1%, a benchmark used by epidemiologists to signal the formal onset of flu season.
“This is the point at which we can say flu season has begun based on activity, not just the calendar,” said Dr. Caitlin Rivers, director of the Center for Outbreak Response Innovation at the Johns Hopkins Bloomberg School of Public Health.
Northeast Emerges as Early Hotspot
At least 14 public health jurisdictions are now reporting moderate to high flu activity, with the heaviest concentration in the Northeast. New York City is experiencing very high activity, while New York and New Jersey are classified as high. Connecticut, Massachusetts, and Rhode Island fall into the moderate category.
Outside the Northeast, flu activity is also high in Louisiana and Colorado, with rising case counts reported in Georgia, South Carolina, Texas, Puerto Rico, and Idaho.
This week also marked a sobering milestone: the first reported pediatric flu death of the season in the United States.
“Influenza activity is clearly increasing right now,” said Dr. Tim Uyeki, chief medical officer of the CDC’s influenza division. “That means the time to get vaccinated is now.”
A Rapid Climb in Severe Cases
State-level data suggest the season may be more severe than usual. In New York, flu cases began rising roughly two weeks earlier than expected, according to Dr. James McDonald, commissioner of the New York State Department of Health.
Hospitalizations in the state have doubled week over week for the past two weeks, a pattern McDonald described as a sharp J-shaped curve.
“That kind of curve indicates people are getting sicker faster,” he said. “We’re seeing more diagnoses and more hospital admissions compared with last year.”
In response, the state issued an alert urging hospitals to intensify infection-control measures and conduct subtype testing.
Subclade K Takes Center Stage
Laboratory surveillance shows that the majority of circulating flu viruses in the U.S. this season belong to subclade K, a variant of the H3N2 strain of influenza A. Historically, seasons dominated by H3N2 are associated with more severe illness, particularly among older adults.
Similar patterns have already emerged internationally. Australia, Japan, China, the United Kingdom, and Canada have all reported early and heavy flu seasons. Australia, where subclade K was first identified, recorded nearly half a million confirmed cases — a national record.
Public health experts often look to Australia’s winter season for clues about what may unfold in the Northern Hemisphere. Still, some caution that flu behavior remains unpredictable.
“If you’ve seen one flu season, you’ve seen one flu season,” said Dr. Jennifer Nuzzo, director of the Pandemic Center at Brown University, noting that back-to-back severe seasons are uncommon.
Others are less optimistic. “I think this could be a pretty bad flu season,” said Dr. Angela Rasmussen, a virologist at the University of Saskatchewan, pointing to Canada’s own early surge.
Vaccine Protection Still Matters
Subclade K was identified after scientists finalized the strains included in this year’s flu vaccines, meaning it is not an exact match. However, experts emphasize that the shots still offer meaningful protection.
Data from the United Kingdom indicate that vaccines reduced the risk of emergency department visits or hospitalization by nearly 75% in children infected with H3N2 strains dominated by subclade K. Effectiveness in adults, particularly those over 65, was lower but still significant at 30% to 40%.
Because most U.S. vaccines are egg-based rather than cell-based, protection levels may differ, experts say. Still, any protection is better than none.
“It takes about a week for immunity to build,” said Dr. Alex Greninger of the University of Washington. “If you get vaccinated now, your immune system should be ready by Christmas.”
Children at Particular Risk
Vaccination coverage among children remains low. CDC data show that only 38% of U.S. children have received a flu shot so far this season, lower than at the same point in each of the past six years.
Last season was the deadliest on record for children, with at least 280 pediatric flu deaths. Nearly 90% of those children were unvaccinated.
Reducing Risk Beyond Vaccination
While flu shots do not completely prevent infection or transmission, they significantly reduce the risk of severe illness. Health experts also recommend layered precautions, particularly as case counts rise.
Masking in crowded indoor spaces, improving ventilation, using air purifiers, and staying home when sick can all reduce transmission. Antiviral medications are available and can shorten illness duration if started within 48 hours of symptom onset.
With flu season gaining momentum, health officials stress that timely action — vaccination, early testing, and practical precautions — will determine how hard the virus hits communities in the weeks ahead.