The flu season worldwide is likely to be nasty, and with the holidays and winter break ahead, a deadly strain of influenza is likely to gain traction in the U.S., according to a UVA Health expert.
The subclade K virus has already started circulating, and it is from the same influenza A lineage that caused the flu pandemic of 1968, killing an estimated 100,000 Americans and a million people worldwide, according to Frederick G. Hayden, MD, a professor emeritus at the University of Virginia School of Medicine.
The strain, H3N2, has circulated since and often sparks severe epidemics that are more likely to cause deaths and hospitalizations than other strains, especially among the elderly and very young.
The fast-spreading subclade K is hitting the United Kingdom hard right now. The UK’s National Health Service has warned that flu hospitalizations are the highest they’ve ever been this time of year.
While flu activity has remained relatively low in the U.S. so far, a Dec. 11 update from the Centers for Disease Control and Prevention suggests the spread of the virus is accelerating, and Hayden believes it could worsen in coming weeks.
In Virginia, respiratory illness activity is currently low, though influenza-related emergency room visits are trending up, according to a Virginia Department of Health dashboard. Virginia has received reports of nine influenza and/or COVID-19 deaths in the past six weeks. There have been no pediatric deaths linked to the flu so far this season.
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Unfortunately, the current vaccines appear to be a poor match for combatting this strain, but any protection is better than none.
In the UK, an early analysis suggests that injected vaccines for adults were only 32 percent to 39 percent effective in preventing influenza-associated emergency department visits and hospitalizations so far this year, while children’s vaccines, primarily the intranasal one, fared better, at 72 percent to 75 percent effective.
“The 2024-25 influenza season, largely due to influenza A H1N1 and H3N2 viruses, was associated with high severity across all age groups, including an exceptionally high number of pediatric deaths,” Hayden said. “Unfortunately, we are seeing the circulation of a new variant of H3N2 virus for which our vaccines may be somewhat less effective.
“However, available vaccines will reduce the risk of serious illness and potentially the spread of this virus.”
Antiviral treatment may reduce the duration of the illness and the risk of complications.
The CDC recommends influenza vaccination for everyone aged 6 months and older with rare exceptions. Vaccines are particularly important for children, those with underlying health conditions including pregnancy, and for seniors, as the immune system’s ability to fend off severe illness fades with age.
“Getting vaccinated as soon as possible remains the single most important action people can do to protect themselves and their families,” Hayden said.