Influenza activity in the United States is on the rise, with the Centers for Disease Control and Prevention (CDC) reporting that 17 jurisdictions—including 14 states, Washington D.C., Puerto Rico, and New York City—identified high or very high levels of influenza-like illness (ILI) in its latest weekly FluView update. The uptick in flu cases signifies a sharp onset of the flu season, with several key indicators showing marked increases.
The agency has reported two new flu-related fatalities among children as well as a growing prevalence of the H3N2 flu virus, particularly its subclade K, just as Americans prepare for numerous holiday gatherings. The number of jurisdictions experiencing high or very high ILI cases surged from five the previous week to a concerning 17. Additionally, the percentage of respiratory viruses testing positive for flu climbed from 8.1% to 14.8%, while outpatient visits for respiratory illnesses rose from 3.2% to 4.1%, surpassing the national baseline of 3.1%.
The CDC noted, “Sustained elevated activity is observed across multiple key activity indicators in many areas of the country.” While the severity of flu-related illnesses remains low at present, the CDC anticipates that influenza activity will persist for several weeks. Of the 927 influenza viruses reported by public health labs, an overwhelming 911 were influenza A, with only 16 classified as influenza B. Among the influenza A viruses that were subtyped, 10.1% were found to be H1N1, with 89.9% identified as H3N2. Alarmingly, 89.8% of the 216 H3N2 viruses characterized since late September were designated as subclade K, which has raised concerns over a potential mismatch with the current seasonal flu vaccine.
The hospitalization rate for respiratory illnesses has also seen a significant jump, from 6.6 to 14.3 per 100,000 residents. Almost 10,000 hospital admissions related to influenza were recorded last week, and flu-related deaths have seen a slight increase from 0.2% to 0.3%. So far this season, the CDC has confirmed three pediatric deaths linked to flu, two of which were attributed to H3 strains.
Seasonally, the CDC estimates there have been at least 4.6 million illnesses, 49,000 hospitalizations, and around 1,900 flu-related deaths this season. It strongly advises everyone aged six months and older who has yet to receive the vaccination to do so promptly. Antiviral medications are also recommended for treating flu and should be administered as quickly as possible, especially to those at greater risk for flu complications.
In related updates, the CDC noted a slight rise in respiratory syncytial virus (RSV) activity in the Southeastern, Southern, and Mid-Atlantic states, particularly among children aged 0-4. While RSV levels remain low overall, the numbers are rising. COVID-19 cases are low but showing an upward trend nationally, with wastewater testing indicating high levels of the virus in several states, including Indiana and Connecticut. Furthermore, cases of whooping cough (pertussis) have remained elevated, though they are lower than their peak in November 2024.
As the holiday season approaches, maintaining awareness of flu activity and vaccination is crucial for public health, encouraging individuals to protect themselves and their loved ones from the virus. The CDC’s next update on flu activity is scheduled for December 30, following the Christmas holiday.