New strain of flu invades Western Pa. amid concerns over vaccine efficacy

A new flu virus variant has been sweeping across the United States, raising questions about the efficacy of this year’s flu vaccines.

Medical professionals in Western Pennsylvania say even though they’re seeing the new flu strain permeate the region, this year’s flu vaccines can still help.

Dr. Amesh Adalja, a Pittsburgh-based infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security, said it’s too early to tell how the vaccine will fare this season.

The new — and potentially severe — strain is called subclade K. It’s a mutated variant of the H3N2 virus (Influenza A).

“There is concern about a vaccine mismatch in the H3N2 component of the vaccine,” Adalja told TribLive. “The vaccine covers three different strains. There does not appear to be a mismatch with the other two, so it is unclear what the overall effectiveness will be until we see which strain dominates in the United States.”

In Britain this year, the vaccine is more than 30% effective — even against the H3N2 strain in adults — in protecting against emergency department visits, according to Adalja.

“It will likely be higher when it comes to protection against more severe disease,” he said.

H3 is now active in Western Pennsylvania.

This year’s vaccine

Dr. Richard Zimmerman is a UPMC physician and vice chair for preventive medicine research in the Department of Family Medicine at the University of Pittsburgh. He said the flu has the potential to “cause a lot of suffering,” especially for older people, those with high-risk conditions and anyone who may be immunocompromised.

The strain K was not around when this year’s flu vaccines were being created in February, Zimmerman said. Now, the frequency of K is 68%, he said, citing the real-time influenza evolution tracker from Nextstrain.org.

“There is no way for the people in February to have guessed K,” Zimmerman said. “It just was not around.”

Not only is K surging in the U.S., but it’s also gaining traction internationally, especially in Japan, Britain and Canada.

Despite K not being around when this year’s flu vaccines were produced, Zimmerman is confident the vaccines have value.

”Depending on the vaccine, we’ll have some coverage — particularly against severe illness,” he said.

It remains to be seen if other strains will also become prominent in Western Pennsylvania, Zimmerman said.

Flu season runs generally from October to April, said Dr. Michael Fiorina, chief medical officer for Independence Heath System. Because it’s just getting started, he believes it’s premature to predict vaccine efficacy for this season.

He said it would be like trying to predict how a baseball game will end in the second or third inning.

“Thankfully, to date, it doesn’t seem like we’ve had any major issues,” he said. “For me to say it’s not effective, that would be very premature. … I don’t know how anyone could hold the belief that it’s more effective or less effective.”

For the 2025-26 season, the influenza vaccine is expected to provide moderate protection with effectiveness against hospitalization — ranging from approximately 42% in older adults to 67% in children, and 43% to 48% in adults overall, according to the Infectious Disease Society of America.

Flu cases on the rise

Influenza is appearing about two weeks earlier this year.

“I usually think of the flu being December, post-Thanksgiving, and it started increasing a lot in the Pittsburgh region last week,” Zimmerman said.

Last year was already an “unusual year” for flu in the region — with all three substrains present, including H3, from which K is derived, Zimmerman said. Usually, only two strains are present in the area.

For H3, symptoms include cough, fever, sore throat and achiness. “For some people, they have a head cold and that’s it,” Zimmerman said. “For others, the virus can actually cause inflammation in the lungs or heart.”

At Independence Health System, Fiorina said a “small amount” of flu cases have come into the hospital, as well as a few hospital admissions. There have been no deaths that he’s aware of to date.

“Fortunately, most of them have been able to be treated with conservative measures and fluids and Tylenol,” he said.

Fiorina said Independence Health System has also seen the flu start one or two weeks earlier this year, similar to Zimmerman’s observations at UPMC.

“It’s within a standard deviation,” he said. “I don’t see that as an outlier. More than a month might pique interest. A week or two? That’s just normal variability.”

At Independence, Fiorina said the main types of Influenza A and B are tested, rather than delving into the subtypes like the H3, which includes the new strain K. The majority of cases that Independence has seen are Influenza A.

The treatment between the strains isn’t different. “I think each and every year is unique. So far, what we’ve experienced this year has been fairly on par with what we’ve had last year,” he said.

Dr. Brian Lamb, internal medicine doctor with Allegheny Health Network, said the health system hasn’t seen a high positive rate of flu yet.

Right now, the infection rate is normal for what AHN usually sees at this time of year.

But Lamb said “we’re starting to see the possibility that it’s not going to be a normal flu season,” thanks to data coming in from the variant K spreading around other countries.

The biggest surge usually happens right after the holiday, during what’s considered peak flu season — January, February and March.

Like Independence, Lamb said AHN doesn’t test specifically for the variants like H3.

“That’s where we rely on advanced government testing to help us,” he said. “A lot of times, they’ll randomly select different positive flus. … It would be cost-prohibitive to check everybody (at AHN).”

But because of the recent government shutdown, Lamb said, Centers for Disease Control and Prevention tracking numbers aren’t up yet and there’s been a lack of guidance.

“A lot of us are in the dark, and then a lot of patients are in the dark about what they should even be doing this year,” he said. “I think people are a little worried about where we are.”

According to Allegheny County’s Influenza Dashboard, 184 influenza cases were reported between Sept. 28 and Nov. 14. The graph shows the numbers climbing weekly.

What concerns Lamb more, however, is the increasing hesitancy to get flu shots.

“That’s the more worrisome thing,” he said. “There’s a lot of questions … there’s just a lot of uncertainty with patients coming in.”

Overall, he sees more confusion surrounding health. “I don’t want to sound political, but really it does come from the political environment that we’re in,” he said. “People are reacting to that. … Most doctors who follow medicine are just frustrated. We’re doing this on our own at this point.”

Preventing infection

Protection against the flu kicks in about two weeks after getting the shot.

But getting a flu vaccine won’t “put a forcefield around your body that prevents the flu from coming to you,” Fiorina said.

“When I get in a car, I put on a seat belt. That seat belt doesn’t prevent me from getting into a car accident … but I think the evidence is irrefutable that it reduces your risk of severe injury,” he continued. “The flu shot is a seat belt for your immune system.”

If someone infected with the flu walked up to Fiorina and coughed in his face, he’s likely going to get the flu, he said, even with a flu shot in his system.

Zimmerman advised that people use proper hand hygiene and test if they get a cough. There are home tests available for flu, he said, and doctor’s office and urgent care centers offer testing.

“Don’t wait too long to get tested, particularly if you’ve got an underlying health condition,” Zimmerman said.

Personally, he will be wearing a mask when he’s on an airplane this week. In addition, he uses an antihistamine nasal spray, which reduces the risk of catching respiratory viruses like the flu.

Fiorina advised using “common sense” recommendations that are always present around flu season.

“As always, wash your hands as frequently as possible,” he said. “Don’t touch your eyes, your nose, your mouth if at all possible.”

Getting plenty of sleep, exercising regularly and eating a nutritious diet can boost the immune system and reduce risk of catching the flu and any viral infection. “If you’re feeling sick, please don’t go out in public,” he said.