By Annette Pinder 

This influenza season has been one of the more severe compared to recent years. According to the U.S. Centers for Disease Control and Prevention (CDC), an estimated 11 million Americans have already been sick with influenza, resulting in about 120,000 hospitalizations and roughly 5,000 deaths. These figures are roughly double those from the 2024–25 season at the same point, when 5.3 million illnesses and 63,000 hospitalizations were reported. 

This flu season’s severity is due to the predominance of a rapidly spreading influenza A (H3N2) virus—a genetic sub-variant called “subclade K.” AP News says H3N2 seasons are typically linked to more serious illness, especially in older adults, and this subclade has become the dominant circulating strain across the U.S., making up more than 90% of typed viruses in many areas. Johns Hopkins Public Health experts say this subtype can spread quickly alongside other winter respiratory viruses, such as RSV and COVID-19, putting extra pressure on hospitals and clinics. These high case counts are worsened by the fact that only 42% of adults and children have been vaccinated this season.  

How Effective Is This Year’s Flu Shot?

As influenza viruses evolve constantly, scientists must predict which strains will circulate months before flu season starts. Thus, the dominant H3N2 subclade K isn’t an exact match to the vaccine strains from last spring, reducing their effect against the current variant. The good news is that our current flu vaccines may still be about 50% effective against overall infection and provide even better protection against severe outcomes, such as hospitalization. Such benefits include: 

  • Reducing the severity of the disease, even if you catch the flu 
  • Preventing hospitalizations and deaths 
  • Protecting against other influenza strains included in the vaccine
     

Is It Too Late to Get a Flu Shot?

No, it is not too late. Health guidance recommends offering vaccination as long as the virus is circulating and the vaccine is available. Although the ideal timing for shots is early in the fall (September–October), people can still benefit from immunization even into January, February, and March. The American Lung Association states that getting vaccinated now can still lower the risk of severe disease and help slow transmission in the community. Furthermore, it takes about two weeks after vaccination for the body to build optimal immune protection, so getting a shot now can still make a meaningful difference in protecting you and those around you during peak flu activity.  

The bottom line is that this year’s flu season is intense because a dominant H3N2 subvariant is spreading widely, combined with lower-than-usual vaccination rates. While the flu shot may not be a perfect match for the circulating strain, it still provides protection—especially against severe illness—and is worth getting now, even midway through the season, as the flu can last well into spring. Public health experts continue to recommend vaccination for everyone 6 months and older, and emphasize that vaccine protection is a valuable tool for reducing the personal and community burden of flu.