December 16, 2025

New Influenza Variant Linked to Rise in Severe Flu Cases   Key Summary: New Influenza Variant (Subclade K) A new influenza A (H3N2) variant, known as subclade K, is linked to rising flu cases and hospitalizations in the U.S., Canada, the U.K., Japan, and Australia Health experts say the variant is now dominant in areas with active influenza spread Subclade K emerged after this season’s flu vaccine was developed, raising concerns about reduced vaccine match Experts stress the variant shows antigenic drift, not antigenic shift, meaning it is not considered pandemic-level The current flu vaccine may be less effective at preventing infection, but it still offers strong protection against severe illness and death CDC data shows influenza activity is increasing nationwide, with 89% of recent samples belonging to subclade K Some regions, including Texas, are seeing rising hospitalizations, especially among adults aged 65 and older Severe flu seasons can occur back-to-back, though they remain relatively uncommon Medical experts emphasize that it is not too late to get vaccinated Public health officials urge continued vaccination, monitoring of symptoms, and preventive measures     Overview: A Mutated Flu Strain Raises Global Concern Health experts are closely monitoring a new influenza A (H3N2) variant, known as subclade K, which appears to be contributing to a rise in flu cases and hospitalizations across several countries, including the United States, the United Kingdom, Canada, Japan, and Australia. Public health officials say this emerging variant may help explain why the current flu season is becoming more severe in some regions. What Is Subclade K? Subclade K is a mutated form of the H3N2 influenza A virus, a strain historically associated with more intense flu seasons. According to infectious disease experts, this variant is now dominant in areas experiencing significant influenza activity. Dr. Andrew Pekosz, a professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, said the variant is being detected widely wherever influenza is spreading in the U.S. Why Experts Are Watching This Variant Closely One major concern is that subclade K emerged after the current flu vaccine was developed, meaning the vaccine may not be a perfect match. Key concerns include: Genetic mutations that may allow the virus to partially evade immune protection Rapid spread across multiple countries Possible links to increased hospitalizations, particularly among older adults However, experts emphasize that the variant represents antigenic drift, a gradual evolutionary change, rather than antigenic shift, which is associated with pandemics.   Does the Current Flu Vaccine Still Work? While the mutations in subclade K may reduce how well the vaccine prevents infection, health experts agree the flu shot still offers important protection, especially against severe illness, hospitalization, and death. “The mutations may allow the virus to evade some—but not all—vaccine-induced protection,” Dr. Pekosz explained. He added that researchers are still determining whether the variant itself causes more severe disease or if rising severity is simply due to higher overall case numbers. Dr. Robert Hopkins, medical director of the National Foundation for Infectious Diseases, echoed this view, noting that influenza remains notoriously difficult to predict. Current Situation in the United States According to the U.S. Centers for Disease Control and Prevention (CDC), influenza activity is increasing nationwide. CDC highlights for early December: Only four states currently report high or very high flu-like illness activity 89% of flu samples collected since late September belong to subclade K National hospitalization rates remain approximately 7 per 100,000, similar to past seasons That said, some states are seeing changes. Texas, for example, has reported rising hospitalizations, particularly among people aged 65 and older, potentially linked to the new variant. Lessons From Recent Severe Flu Seasons The 2024–2025 flu season ranked among the most severe in decades. While consecutive severe seasons are uncommon, health experts stress they are not unprecedented. High circulation of aggressive strains like H3N2, combined with lower immunity and vaccine mismatches, can contribute to challenging flu years. Public Health Message: Don’t Delay Vaccination Despite uncertainties surrounding subclade K, experts agree on one point: vaccination still matters. “It is not too late to get a flu shot,” Dr. Pekosz said, stressing that even partial protection can significantly reduce serious outcomes. Public health officials continue to recommend: Getting vaccinated as soon as possible Monitoring symptoms closely, especially in older adults Practicing basic prevention, such as handwashing and staying home when ill What Happens Next? Researchers are actively studying whether subclade K leads to more severe disease on an individual level or whether its impact is primarily due to widespread transmission. As the flu season progresses toward its typical peak in January and February, health authorities say surveillance and vaccination will remain critical tools in reducing the burden of illness.

Flu-Related Deaths of Three Children in Ottawa Signal a Severe Influenza Season in Ontario   Quick Summary: Key Facts at a Glance Three children aged 5–9 have died from influenza-related complications in Ottawa and Eastern Ontario within the first two weeks of December Health officials say the deaths are unusual and may signal a severe and early flu season Influenza A (H3N2) is the dominant circulating strain and is spreading rapidly among children and teens Pediatric hospitals, including CHEO, are seeing record-high flu cases, emergency visits, and admissions Ontario ICU admissions due to influenza increased by 127% in just one week Nationwide, over 20% of flu tests are now positive, with the highest rates among people under 19 Medical experts warn that low vaccine uptake and partial strain mismatch may worsen outcomes Flu vaccination remains highly effective at preventing severe illness, hospitalization, and death Public health officials urge immediate vaccination, especially before holiday gatherings Overview: A Tragic Warning as Influenza Cases Surge Health officials in Ottawa and Eastern Ontario have confirmed the deaths of three children aged between five and nine due to influenza-related complications during the first two weeks of December. Medical officers describe the situation as unusual and alarming, highlighting concerns that the current flu season could be more aggressive than recent years. The deaths have prompted urgent warnings from Ottawa Public Health and the Eastern Ontario Health Unit, as hospitals report rapidly increasing influenza activity—particularly among children and adolescents.   Sharp Rise in Influenza A Across Ontario According to regional health authorities, there has been a rapid and significant increase in influenza A, particularly the H3N2 subtype, which is historically linked to more severe flu seasons. Key indicators include: Influenza test positivity rates exceeding 20% nationwide Ontario positivity rates nearing 26%, higher than any of the last three seasons Children under 19 account for the majority of positive cases Hospital admissions and ICU cases are rising sharply The Children’s Hospital of Eastern Ontario (CHEO) has reported exceptionally high pediatric flu cases, far exceeding seasonal norms. Pediatric Hospitals Under Pressure CHEO confirmed that: Over 300 children tested positive for influenza in the first 10 days of December Only 11 cases were recorded during the same period last year Emergency departments are seeing 220–280 visits per day Daily hospital admissions for flu-related illness continue to climb Other children’s hospitals across Toronto, Waterloo, Calgary, and Montreal report similar trends, signaling a nationwide pediatric influenza wave. ICU Admissions Jump 127% in One Week The Ontario Hospital Association reported a 127% increase in influenza-related ICU admissions in just one week. Hospitalizations rose by 84%, while confirmed flu cases increased by 150% during the same period. Health leaders stress that while COVID-19 and RSV levels remain relatively stable, influenza is now the dominant respiratory threat. Why This Flu Season Is Hitting Children Hard Experts attribute the severity to multiple overlapping factors: 1. Dominance of Influenza A (H3N2) Many children have little or no prior exposure to H3N2 Lower natural immunity increases susceptibility 2. Vaccine Mismatch Concerns The circulating strain differs genetically from vaccine strains However, vaccines still significantly reduce severe illness and hospitalization 3. Declining Vaccination Rates Public health officials report lower flu vaccine uptake Only 25% of hospitalized children in past studies were vaccinated What the Data Shows Nationwide Federal surveillance highlights troubling trends: 6,799 confirmed influenza cases in early December 1,850 flu-related hospitalizations Children aged 5–11 are showing positivity rates near 64% Teens aged 12–19 exceeding 50% positivity Health experts describe these levels as “sky-high. Vaccination Remains the Strongest Defense Despite concerns about strain mismatch, medical experts emphasize that the influenza vaccine remains highly effective at preventing severe outcomes: Up to 75% effectiveness in preventing hospital visits among children 30–40% effectiveness in adults Reduces risk of ICU admission, pneumonia, and death Since immunity takes approximately two weeks to develop, officials urge families to get vaccinated before holiday gatherings. Who Is Most at Risk? While most people recover from the flu, severe complications are more likely among: Children under five Adults over 65 Individuals with chronic illness or compromised immune systems Unvaccinated populations Health officials warn that early surges in children often precede severe outbreaks among older adults. Preventive Measures Beyond Vaccination Public health authorities recommend additional precautions: Frequent handwashing Avoiding face-touching Staying home when sick Wearing masks in healthcare settings when required Avoiding hospital and long-term care visits while ill These measures help reduce transmission during periods of high viral circulation. A Season That May Worsen Before It Improves Medical experts caution that the flu season is far from over, with peak transmission expected mid-to-late December in several regions. “The sooner you get vaccinated, the better,” experts stress, warning that continued spread could lead to more severe outcomes among vulnerable populations, including seniors in long-term care. Final Word: A Preventable Tragedy The deaths of three children in Eastern Ontario serve as a sobering reminder that influenza is not a mild illness for everyone. Health leaders emphasize that vaccination, awareness, and early action remain critical tools in preventing further loss of life during what may be one of Canada’s most challenging flu seasons in years. References: https://www.cbc.ca/news/health/kids-teens-flu-deaths-ontario-9.7018018 https://www.theglobeandmail.com/canada/article-three-children-dead-ottawa-eastern-ontario-region-flu-related/