A new strain of the flu virus, known as influenza subclade K, has become the dominant type circulating in the United States ahead of the holiday season. According to Dr. Shalika Katugaha, system director of Infectious Diseases for Baptist Health, this variant is a mutated version of the H3N2 flu virus and has already caused increases in flu cases in countries such as Canada, Japan, and the United Kingdom.
“The influenza virus frequently mutates, resulting in new variants and subclades each season,” Dr. Katugaha said. “This particular strain is a mutated version of the H3N2 flu virus.”
The symptoms associated with subclade K are similar to other flu viruses and include fever, chills, body aches, headache, fatigue, congestion, runny nose, and cough.
“Historically, influenza A (H3N2) seasons are associated with higher hospitalization and mortality rates in older adults. The concern is that subclade K, as a mutated H3N2, will follow that pattern, resulting in a more severe flu season,” Dr. Katugaha said. “Health officials residing in areas where the subclade K variant has become dominant have reported serious illnesses, especially in vulnerable populations like the elderly and young children.”
Regarding this year’s flu vaccine effectiveness against subclade K, Dr. Katugaha explained that while the vaccine was updated earlier this year to target expected strains at that time, it does not specifically match subclade K because this variant appeared more recently.
“The virus mutations have lessened the effectiveness of the vaccine, leading to updated recommendations for the next season,” she explained. “That said, the vaccine still provides substantial protection, especially against severe outcomes and hospitalizations. Additionally, this year’s flu shot is expected to match the circulating H1N1 and influenza B strains well.”
She added: “It’s not too late to get the flu vaccine. It typically takes the body two weeks to develop immunity so plan to get it as soon as possible!”
To reduce risk during holiday gatherings when cold and flu viruses spread easily indoors among families and friends—especially those who are older or very young—Dr. Katugaha recommends frequent handwashing; cleaning commonly touched surfaces; staying home if sick; and considering antiviral medication for high-risk individuals after exposure.
“Certain high-risk individuals may benefit from a prophylactic antiviral treatment if they’re exposed to the flu,” Dr. Katugaha added. “Talk to your primary care physician if you’d like to learn more.”
Baptist Health encourages people who need a vaccine or fall ill with flu symptoms to contact their primary care provider for assistance.
