Flu season is in full swing, but this year, it’s worse than usual due to a new strain.
The Indiana Department of Health reports that flu activity in Indiana is currently “very high.” That’s due to a new strain, “subclade K,” an influenza A virus that is part of the H3N2 family; it’s often been associated with more severe flu seasons.
Tom Hrisomalos, MD, infection disease specialist with Indiana University Health, said the “subclade K” strain accounts for about 90 percent of cases. The rest is made up of H1N1 strains and the Influenza B virus.
More than seven million people in the country have contracted the flu since October; about 3,100 people have died from the flu.
In Indiana, 17 flu-related deaths have been reported so far. Twelve of those were in people older than 65.
“We worry [about] our young kids, because they don't have a lot of immunity; they haven't been exposed to influenza a lot and so there's not preexisting immunity. And by that, I mean age zero to four is a high-risk group,” he said. “And then older adults, particularly over age 65, and then anyone who's got preexisting conditions would increase their risk of having more severe influenza.”
Hrisomalos said there has been an increase in visits to the emergency department, urgent care and primary care offices in the last couple weeks. Hospitalizations have also increased, but Hrisomalos says this isn’t outside the norm for flu seasons.
It’s hard for a vaccine to perfectly match the current strain when it’s developed before the season begins, Hrisomalos said. The flu vaccine was developed in early 2025, but the subclade K strain wasn’t detected until August.
This year’s flu vaccine covers three strains, including an H3N2 strain.
“I think what we'll find is this vaccine is probably about average for influenza vaccines,” Hrisomalos said. “Seasonally, it's not going to be a poor match, but it may not be the absolute best match, but I think it will be beneficial. And for those individuals who have not yet been vaccinated, it's not too late.”
According to data for the Centers for Disease Control and Prevention, flu vaccine doses are down from last year. The most recent data reported from Dec. 7 to Dec. 13, 2025, there were just over 130.7 million doses of the flu vaccine administered. At about the same time in 2024, nearly 143.8 million doses were administered.
Hrisomalos said people still have time to get vaccinated; the current spike is likely to last a few weeks. The vaccine can prevent sickness for most people; for those who do get the flu, the vaccine helps make symptoms milder and decreases the duration of sickness and risk of hospitalization.
As for COVID-19, while there hasn’t yet been a spike, infections are growing in over 30 states, including Indiana. As of Dec. 29, the Indiana COVID-19 Wastewater Dashboard shows a spike in the amount of the virus present in wastewater statewide.
“It has mutated over the last few years, and with that mutation, it has become more transmissible,” he said. “It spreads easier, but the severity of illness of the current strains has decreased quite a bit, and it's much milder.”
To avoid getting sick, Hrisomalos recommends people wash their hands, cover their coughs and wear masks in crowded settings.
