Flu Season Update: A Glimmer of Hope
Flu cases are rising across much of the United States, but there’s a bit of good news amidst this tough season: the flu shot might be more effective than previously thought.
Early indicators suggest that this season’s vaccine offers protection against the H3N2 subclade K strain that’s been spreading widely. Interestingly, this strain emerged last summer, after production of the 2025-2026 vaccine had already begun.
Scott Hensley, a microbiology professor at the University of Pennsylvania, remarked, “This is unexpected good news. Although it’s not a perfect match with what’s circulating, the vaccine seems to stimulate the production of antibodies that can provide some level of protection.”
Every year, the Penn Centers of Excellence for Influenza Research and Response conducts an early assessment of how effectively the seasonal flu shot generates an antibody response in the immune system. Essentially, they gauge how likely the vaccine is to provide tangible protection for most people.
Findings from this year’s analysis, shared recently on the preprint server medRxiv, revealed intriguing insights. The current flu vaccine targets three strains: two A strains (H1N1 and H3N2) and one B strain. However, a slight change in H3N2 last June raised concerns about how well the shots would align with circulating strains.
In October and November, researchers examined blood samples from 76 individuals between ages 24 to 81, taking one sample before vaccination and another about a month later. Initially, 39% had antibodies against H3N2, likely from prior exposure. After vaccination, that number jumped to 71%.
The response was even more notable regarding the shifted H3N2 strain, subclade K. Before the shot, only 11% had antibodies against this specific strain, but that nearly quadrupled to 39% post-vaccination.
This effectiveness didn’t seem to vary with age among participants.
Doctor visits for flu-like symptoms are at their highest levels for this time of year in nearly 30 years. The latest data from the CDC indicates that nearly 1 in 10 outpatient visits were for flu symptoms as of December 27.
Even though vaccinated individuals can still catch the flu, their symptoms tend to be significantly milder compared to those who are unvaccinated.
Angela Rasmussen, a virologist at the University of Saskatchewan, stated, “This confirms that the vaccine can still offer better protection against H3N2 than being unvaccinated. The mismatch may not be as significant as previously worried.”
Bill Hanage, a professor at Harvard T.H. Chan School of Public Health, added, “It’s more evidence that while the current vaccine may not be flawless, it provides effective protection, particularly against serious illness.” Neither Hanage nor Rasmussen were part of the recent research.
Hensley described flu strains as “master shapeshifters,” which is part of why it’s always tricky to get vaccines to align perfectly with the exact strains in any given year.
The recent findings are important, especially considering the record number of pediatric flu deaths from last season, which Hanage noted. The CDC recently reported an additional childhood death, bringing the total to 289, surpassing even the pediatric deaths from the 2009 H1N1 pandemic.
This week, the Department of Health announced it would not continue recommending annual flu shots for children. Yet, the CDC maintains on its website that “everyone 6 months and older, with rare exceptions, should receive a flu vaccine.”
As of December 27, only 42.5% of kids had received their flu shot this year—this is the lowest rate recorded by the end of December since at least 2019.
Rasmussen emphasized, “Vaccines won’t help if people don’t get them. It’s not too late. Everyone reading should remember to get a flu shot if they haven’t done so already.”
