Flu cases rise in multiple regions as holiday gatherings drive transmission

Flu activity is rising across the United States, led by New York, Colorado, New Jersey and Louisiana, according to data from the Centers for Disease Control and Prevention. For the week ending Dec. 6, New York City officials classified flu transmission as very high, the top category, underscoring how dense urban areas can accelerate spread. In New Jersey, Hackensack Meridian Health said flu test positivity across its emergency departments, urgent cares and physician offices sits around 30%, compared with roughly 2% to 3% for COVID-19 and RSV.

Elisabeth Marnik, chief science officer at Those Nerdy Girls, said overall influenza activity is increasing based on wastewater monitoring and the CDC influenza dashboard, but she cautioned the burden is not uniform across the country. Dr. Daniel Varga, chief physician officer at Hackensack Meridian Health, noted that population density in New York and New Jersey raises the risk of accelerated transmission. Data through the CDC show many kids are currently sick, and doctors warn the wave can spread through families after gatherings around Thanksgiving and during the holiday season.

Dr. Neal Shipley, medical director of Northwell Health-GoHealth Urgent Care in New York, said flu activity jumped quickly after Thanksgiving, rising from near silence to a sharp uptick. He noted this pattern has recurred in recent seasons and tends to occur after holidays when people travel and socialize. Health officials point to a virus mutation driving the current surge: a flu strain known as H3N2 that appears more transmissible than older versions.

Elisabeth Marnik said the H3N2 strain now accounts for about 85% to 86% of current cases, and the virus has changed enough that the immune system may recognize it less readily. That mutation, along with high social mixing during holidays, has contributed to the broader rise in cases this season. Dr. Shipley added that the rapid early rise mirrors effects seen in prior years, and House calls for vigilance remain high.

Vaccination remains a central defense, though experts caution about effectiveness that varies by age. Current data show the vaccine is about 30% to 50% effective in preventing hospitalization in adults and about 70% to 75% in children. Still, officials emphasize that vaccination can reduce the severity of illness and the likelihood of hospitalization and death. "Flu is a respiratory pathogen, so masking is a really great strategy for people, especially in crowded spaces like airports or trains," Marnik said. She also recommended improving ventilation and using air filtration when possible, along with good hand hygiene and sufficient sleep to bolster defenses.

In addition to vaccination and masking, antiviral treatments are available for high-risk populations and work best when started early in the course of illness. People who suspect they have the flu should get tested promptly so they can qualify for treatment that can shorten illness and reduce spread. If symptoms worsen—such as trouble breathing, chest pains or an ongoing fever—medical attention should be sought promptly.

The flu season remains dangerous for some groups. Officials note that flu can lead to serious complications, including bacterial pneumonia, and last year the United States recorded hundreds of thousands of hospitalizations due to influenza. The burden has already shown signs of being severe in some parts of the country, with pediatric deaths reported in Colorado and North Carolina this season. Health experts also point to last year as a cautionary benchmark: one of the worst seasons on record for pediatric deaths, a peak many fear could be matched this year if transmission stays high.

Those at higher risk include people over 65, children under 4, individuals with asthma or heart disease, and pregnant people. Public health officials urge people to consider vaccination now, especially as cases are expected to stay elevated for several more weeks and possibly rise again after Christmas and New Year’s before gradually slowing in late January and possibly continuing into the spring.