12/24/2025
The most widespread flu variant in Louisiana this season is the Influenza A(H3N2) subclade K. This year's flu shots do work against it, but their effectiveness in preventing infection may be reduced due to mutations that developed after the vaccine was formulated.
Widespread Variant in Louisiana
Louisiana has reported high or very high flu activity driven primarily by the Influenza A(H3N2) virus, and specifically a new, more contagious variant within that subtype known as subclade K. This variant has several mutations on its surface protein, making it slightly different from the A(H3N2) strain included in the vaccine.
Effectiveness of This Year's Flu Shot
The current flu vaccine for the 2025-2026 season is trivalent, meaning it is designed to protect against three main seasonal flu types:
Influenza A(H1N1)
Influenza A(H3N2)
Influenza B (Victoria lineage)
While the vaccine contains a general H3N2 component, the genetic "drift" of the subclade K variant means the vaccine is not a perfect match for the dominant circulating strain.
Key points on vaccine effectiveness:
Reduced Protection from Infection: The mismatch may lower the vaccine's ability to prevent infection from the subclade K strain entirely.
Significant Protection against Severe Illness: Despite the mismatch, health experts emphasize the vaccine is still effective at preventing severe outcomes, including hospitalization and death.
Protection Against Other Strains: The vaccine provides good protection against the H1N1 and Influenza B strains, which are also circulating.
Doctors in Louisiana and the CDC strongly urge people to still get vaccinated, as it offers the best available protection against serious illness and helps reduce the overall burden on the healthcare system. You can find more information on flu activity and vaccination recommendations on the CDC website or the Louisiana Department of Health website.