Flu on the Rise Across the U.S., With Some Regions Hit Hard

The flu season is intensifying across the United States, with several states reporting higher activity and New York City in the top category for transmission. The Centers for Disease Control and Prevention data for the week ending Dec. 6 show New York, Colorado, New Jersey and Louisiana in the high category, while New York City is reporting flu levels at the very high level—the highest tier.

Hackensack Meridian Health’s emergency departments, urgent cares and physician offices are seeing a 30% test positivity for flu, compared with about 2-3% for COVID and RSV, a disparity health officials say reflects the virulence of the current strain and the crowded conditions of some metropolitan areas. Elisabeth Marnik, chief science officer at Those Nerdy Girls, said that across wastewater monitoring systems and the CDC’s influenza dashboard, overall influenza cases are increasing. “In general ... if we look at the different wastewater monitoring systems, or if we look at the CDC’s influenza dashboard, we see that overall cases of influenza across the country are increasing,” she noted. But she added that the burden is not uniform, with some regions seeing sharper surges than others.

Experts say population density in New York and New Jersey can accelerate transmission, and the current wave is being felt nationwide with varying intensity. Dr. Daniel Varga, chief physician officer at Hackensack Meridian Health, said the high positivity in dense urban areas highlights how quickly flu can spread in crowded spaces when people are traveling, gathering and staying indoors during the colder months. He noted that New York City, in particular, faces a higher risk of rapid transmission due to its population density. Data through the CDC show that many other states remain in the moderate range, including Connecticut, Idaho, South Carolina, Georgia, Michigan, Texas, Massachusetts and Puerto Rico.

The flu is noticeably affecting children as well. Dr. Neal Shipley, medical director of Northwell Health-GoHealth Urgent Care in New York, said the season has already seen a rapid uptick after Thanksgiving: “We went from having almost no flu activity to, right after Thanksgiving ... a pretty sharp uptick.” He added that this pattern has been observed in recent seasons, including 2023, and is typical of respiratory illnesses that spike after holiday gatherings and travel. “It’s kind of dispersed throughout the country right now,” Marnik observed, but emphasized that the timing after holidays means a six-week window of sustained activity, with cases potentially rising again in the week or two after Christmas and New Year’s before waning toward late January. She cautioned that flu season can linger well into spring.

Beyond the current wave, experts point to a mutation in the flu virus as a key driver of the high activity this season. Marnik said the predominant strain is H3N2, which has “changed a lot from prior versions of the flu,” reducing the immune system’s ability to recognize it. Shipley added that about 85-86% of current cases are attributed to this mutated H3N2 strain, helping explain why transmission has been so brisk in communities across the country. Varga also suggested that vaccine hesitancy may have contributed to the season’s severity, noting that hesitancy could help explain a more rapid rise and higher hospital loads once the season takes hold.

The vaccine remains a critical tool. Shipley said the vaccine’s effectiveness, while not perfect, still protects against hospitalization: roughly 30% to 50% effective in adults at preventing hospitalization and about 70% to 75% effective in children. He stressed that protection is better than no protection and that receiving the shot can reduce the risk of severe illness and the spread to others. Public health officials also emphasize that vaccination is a population-protective measure, helping to shield vulnerable groups.

At-home tests are widely available and can help people determine whether they have the flu, but doctors encourage people to seek medical advice promptly if they are in high-risk groups or develop concerning symptoms. Antiviral treatments are available for high-risk populations and work best when started early in the course of illness. Shipley urged people to get tested early so they can determine if they qualify for treatment and to reduce the chance of spreading the virus to others. If symptoms escalate—difficulty breathing, chest pains, a persistent fever—medical attention should be sought promptly.

The current flu season remains dangerous for certain groups. Officials remind that flu can lead to complications, including pneumonia, and last year saw about 400,000 hospitalizations nationwide. Tens of thousands of people die from influenza each year, and states including Colorado and North Carolina have already reported pediatric flu deaths this season. Those at higher risk include adults aged 65 and older, children under four, people with chronic conditions such as asthma or heart disease, and pregnant people.

Public health guidance continues to emphasize layered protections. Masking in crowded spaces, particularly with a well-fitted N95, is recommended in settings where transmission risk is high. Improving ventilation—opening windows where possible, using air filters, and avoiding overly crowded indoor spaces—can also help reduce spread. Good hygiene remains important: frequent hand washing, cleaning high-touch surfaces, adequate sleep, and regular exercise can support the body’s defenses. As Marnik noted, the flu is an airborne pathogen, so what people breathe is a primary route of infection, making these measures especially relevant during peak season.

Health officials reiterate that it’s not too late to get a flu shot. While effectiveness varies by age group, even partial protection can prevent hospitalization and death, reduce the overall burden on the health care system and curb community spread. The season’s trajectory remains uncertain, but the combination of a predominant H3N2 mutation, holiday-related surges and varying regional activity has already made this one of the more challenging flu seasons in recent years.