Hailey Waldo
ECB Publishing, Inc.
As influenza activity continues to rise across the United States this winter, health officials are closely monitoring a variant of the seasonal flu virus known as H3N2 subclade K, which is now the dominant form of influenza A circulating in the country. Florida residents are being urged to stay informed about the strain and its symptoms, as well as steps they can take to protect themselves and others.
Influenza A viruses have long been a major contributor to seasonal flu, but this year’s version carries subtle genetic changes that make it different from strains targeted by the current flu vaccine. The Centers for Disease Control and Prevention (CDC) reports that out of the influenza A (H3N2) viruses it has genetically examined so far this season, nearly nine out of every 10 belonged to subclade K, meaning the vast majority of H3N2 viruses circulating in the U.S. have this mutation.
This high number shows a trend seen internationally with at least 7.5 million illnesses, 81,000 hospitalizations and 3,100 deaths from influenza according to the CDC. The H3N2 subclade K strain emerged earlier in the year overseas and has since become widespread, though its exact impact and severity remains under study by the World Health Organization (WHO).
Florida health authorities confirm that flu activity is elevated in many parts of the state and that the strain identified in many U.S. cases, including subclade K, has been reported in Florida as well as more than a dozen other states this season. While the Florida Department of Health does not publicly break down state flu detections by subclade percentages in weekly reports, it continues routine surveillance to track trends, outbreaks and the onset and peak of the flu season locally.
What this means in practical terms, experts say, is that most influenza A viruses now circulating like H3N2 subclade K in terms of genetics, which helps explain this year’s increased spread. National surveillance data indicate flu activity across many regions is above baseline and expected to continue rising in December and January, the peak months of flu season.
The symptoms associated with this strain are similar to traditional influenza infections. People sick with H3N2 subclade K commonly experience sudden onset of fever, chills, cough, sore throat, body aches, headache, fatigue and congestion, much like previous seasons. Loss of appetite and nausea can occur in some patients, especially children. Health officials emphasize that severe symptoms, such as difficulty breathing, chest pain, confusion, dizziness, or persistent high fever, warrant immediate medical evaluation.
The current seasonal flu vaccine was formulated before the subclade K strain became widespread, and genetic changes in the virus mean a precise match was not achieved in all cases. However, vaccinations continue to provide protection, especially against serious complications, hospitalizations and deaths, according to the WHO.
In Florida, flu activity typically peaks during the peak of winter, and current surveillance shows outpatient visits and lab detections rising steadily.
Officials also urge residents to practice preventive measures, including frequent hand-washing, covering coughs and sneezes, staying home when ill and talking with a healthcare provider about antiviral treatments particularly for high-risk people such as older adults, young children, pregnant people and those with chronic health conditions.
While specific percentages of subclade are not yet available for every county, the H3N2 subclade K strain is widespread in the United States and present in Florida, and it is contributing to higher flu activity this season. Health departments at both the state and federal level will continue to update the public as more data become available.