BREAKING: Subclade K Influenza is Escaping Flu Shot Protection

A week ago we warned you about Subclade K influenza—a H3N2 variant with seven new mutations. This genetic “drift” emerged after this year’s flu vaccine was created. There is growing concern that this variant could escape vaccine protection. That’s because it only takes a couple of mutations to escape prior protection. If you wait for the CDC to alert you that Subclade K influenza is taking over and poses a serious risk, there is a good likelihood that you will be weeks behind this virus.

America’s influenza surveillance system is always delayed, but early signs suggest that the gap between what’s happening in communities and what appears in official reports is wider than ever. That’s partly because the CDC is short staffed and the government shutdown slowed things down even more. The most recent Fluview from the CDC (Nov. 15, 2025) reports that:

“Seasonal influenza activity remains low nationally but is increasing, primarily among children.”

I am not sure I trust this report, though. Let me explain why.

Why the Subclade K Influenza Variant Could Pose a Problem:

First, let’s turn to Australia and other countries in the southern hemisphere. It was a bad flu season there! We have reported extensively on what happened during their winter flu season at this link. That was before the Subclade K influenza virus underwent genetic changes. Those alterations could make people in North America even more vulnerable than our Australian counterparts.

We don’t know yet if the Subclade K flu will be worse than their influenza A(H3N2) virus. We do suspect, though, that this year’s flu shot will be less protective for us than the vaccines used in Australia. Those were a fairly good match for the circulating virus there. And yet the Aussies still suffered badly.

An early publication in the Journal of the Association of Medical Microbiology and Infectious Disease Canada (Oct. 31, 2025) points out that:

“After a period of minimal change following the COVID-19 pandemic, influenza A(H3N2) viruses started to evolve in important ways during the northern hemisphere’s 2024–2025 influenza season. During the southern hemisphere’s 2025 influenza season, a further evolved and vaccine mismatched A(H3N2) variant arose and is projected to predominate during the northern hemisphere’s 2025–2026 influenza season. While mismatched vaccines can still provide protection against circulating variants, enhanced surveillance is warranted including timely influenza virus sequencing and vaccine effectiveness monitoring to inform risk assessment and response.”

Is the CDC “Flying Blind”?

CIDRAP is the Center for Infectious Disease Research and Policy at the University of Minnesota. Its mission is to:

“prevent illness and death from infectious diseases through epidemiological research and rapid translation of scientific information into real-world practical applications and solutions.”

On November 12, 2025 a CIDRAP release about the upcoming uncertainty about the Subclade K influenza outbreak quotes a key Canadian epidemiologist:

“‘This is not the time to be flying blind into the respiratory virus season,’ Danuta Skowronski, MD, the epidemiology lead for influenza and emerging respiratory pathogens at the British Columbia Centre for Disease Control, told CIDRAP News.

“‘We look to the US to see what is circulating, because it drives what’s going on in North America,’ she said.”

“The US Centers for Disease Control (CDC) has not posted the standard weekly respiratory illness surveillance data since September 26, and it is unknown when or if national surveillance in the country will resume.”

As described above, the CDC has updated its Fluview oversight on November 15, but it is still behind and won’t issue a new report until December 1.

Why We Are Concerned About Subclade K Influenza:

We are big fans of scientific data. That requires widespread testing. Until results becomes available, though, we have to rely upon other sources of information. It turns out that Walgreens has launched its Respiratory Illness Index. The pharmacy chain uses over-the-counter product purchases, prescription data and testing to offer respiratory illness trends across the U.S. This tool is crude, but it offers some sense of what is happening in the real world. Texas is a hot spot, along with New York and Michigan.

We are awaiting data from the WastewaterSCAN Dashboard to get more detailed influenza information. What we can tell you is that another nasty pathogen, norovirus, is widespread. The wastewater testing program reports that this “winter vomiting disease aka cruise ship virus” has increased by 69% since last month. If you would like to get a sense of what norovirus is like, here is a link.

Family gatherings offer a wonderful opportunity for viruses to spread. We suspect that Thanksgiving travel has enabled both Subclade K influenza and norovirus to migrate far and wide. Christmas shopping, sporting events and lots of parties will also facilitate the transmission of a variety of infections.

The CDC reported that the 2024-2025 flu season was the worst the U.S. has seen since 2010. Given that Subclade K influenza seems to be evading protection from the vaccines, it is entirely possible that we will follow Australia’s example and have a tough time over coming weeks.

Your Subclade K Influenza Protection Strategy:

We suggested last week that you be prepared to test immediately upon experiencing symptoms such as fever, sore throat, aches and pains, cough and fatigue. We make no recommendations about particular tests, but here are some options:

• iHealth COVID-19, Flu A&B 3-in1 Antigen Rapid Test  

• OSOM Covid Flu Test Combo – 3-in-1 Rapid Flu A B and Covid Home Test Kit

• CorDx TyFast 10 Mins Flu A/B & Covid 19 Multiplex Rapid Test

The People’s Pharmacy is reader supported. When you buy through links in this post, we may earn a small affiliate commission (at no cost to you).

Whatever test kit you buy, we think it makes sense to have a kit available just in case someone starts to experience classic symptoms such as fever, nasal congestion, sore throat, fatigue and body aches. That’s because antiviral drugs could make a difference, especially if someone is immunocompromised or vulnerable to infection. The Subclade K flu variant should still be susceptible to antiviral medicine.

If you test positive for flu, your doctor may prescribe an antiviral drug, especially if you are at high risk:

• Oseltamivir (Tamiflu) – oral medication, taken twice daily for 5 days
• Zanamivir (Relenza) – inhaled powder (not recommended for people with asthma or COPD)
• Baloxavir (Xofluza) – single-dose oral medication
• Peramivir (Rapivab) – IV administration in healthcare settings

Other Steps to Take:

• If you’re sick, stay home. Do not spread the virus to friends or family, even for holiday celebrations
• Wear high-quality N95 masks in crowded indoor spaces, especially if you’re at high risk
• Wash hands thoroughly and frequently for at least 20 seconds
• Consider a portable CO2 meter for checking air quality in public spaces. Poor ventilation increases infection risk for all respiratory viruses
• Upgrade your home air filters to high-efficiency models

Support Your Immune System

Listen to our interview with Dr. Roger Seheult for evidence-based strategies on strengthening immune function and what to do if you catch the flu. Here is a link to that podcast.

The Bigger Picture: It’s Not Just Flu

Remember, Subclade K influenza is just one of many respiratory viruses circulating this winter. Others include:

• SARS-CoV-2 (COVID-19)
• RSV (Respiratory Syncytial Virus)
• Human Metapneumovirus (HMPV)
• Mycoplasma pneumoniae (walking pneumonia)
• Pertussis (whooping cough)
• Multiple cold viruses

Your ability to avoid infection depends partly on your immune system, but even extremely healthy people can catch these infections. Our eGuide to Colds, Coughs & the Flu can help you deal with symptoms if you do get sick this winter. Find it under the Health eGuides tab.

Final Words:

We hope for a mild flu season, but the warning signs are concerning. Subclade K influenza represents a significant evolution of H3N2 that has already caused early, intense flu seasons in Japan, South Korea, the United Kingdom and Canada. With vaccine effectiveness lower than hoped for and holiday travel accelerating spread, we could be facing a challenging winter.

We will be tracking this flu variant as it spreads across the US in coming weeks. And we will do our best to assess vaccine effectiveness, though it may take several more weeks before we have an answer to that question.

Most people still haven’t heard about Subclade K influenza. Many assume their flu shot will work as well as in past years, which hasn’t been all that great. They may be surprised when symptoms appear despite vaccination. Share this article with friends and family to help them prepare for what could be ahead.

Thank you for trusting The People’s Pharmacy to keep you informed and prepared. Please stay healthy this winter.