H3N2 is a subtype of influenza A that can cause severe flu seasons, particularly among older adults, young children, and people with chronic health conditions, and recent data indicates Canada may face a challenging flu season due to an evolving form of H3N2.
H3N2
The virus mutates frequently, which can lead to changes in severity and potential mismatches with seasonal vaccines
Symptoms and Complications
Infection with H3N2 typically lasts 5–7 days, though a severe cough may persist for up to three weeks. Common symptoms include:
- Fever and chills
- Body aches and headaches
- Sore throat and cough
- Exhaustion
- Minor nasal congestion
- Vomiting and diarrhea, more common in children
Serious complications can occur, even in otherwise healthy individuals, and include pneumonia, acute respiratory distress syndrome, sepsis, meningitis, and myocarditis
Risk Factors
People at higher risk of severe outcomes from H3N2 infection include:
- Children under 5 years
- Adults 65 years and older
- Pregnant individuals
- People with chronic conditions such as asthma, diabetes, heart disease, immunosuppression, or neurological conditions
Diagnosis and Treatment
H3N2 influenza is diagnosed by a healthcare provider using symptom assessment, physical examination, and sometimes rapid flu tests from nasal or throat swabs. Antiviral medications, such as Tamiflu or Relenza, are most effective if administered within the first 48 hours of symptom onset
Supportive care, including rest, hydration, and over-the-counter symptom relief, is crucial, while antibiotics are only necessary in the case of secondary bacterial infections.
Prevention
Preventive measures include:
- Receiving the annual flu vaccine, which reduces severity and mortality
- Practicing good respiratory hygiene: covering mouth and nose when coughing or sneezing, frequent handwashing, and avoiding touching the face
- Avoiding close contact with infected individuals and staying home when sick
- Using protective equipment and hygiene when in contact with pigs, as certain H3N2 variants originate in swine
Vaccines for influenza cannot cause the flu because they contain only protein components of the virus
Current Situation in Canada
Flu cases are rising in Canada, and experts warn that the 2025 – 2026 season could be particularly severe due to a mutated H3N2 strain, which may have structural changes making it partially mismatched with the current vaccine. Early indicators from the Southern Hemisphere and parts of Europe and Asia suggest potential record high case counts. In Canada, older adults and school-aged children are at higher risk for severe infection
Public health authorities advise Canadians, especially seniors, to get vaccinated and consider combining flu shots with other seasonal vaccines such as COVID-19 or RSV vaccines where eligible. Although vaccine coverage may not perfectly match the circulating H3N2 variant, vaccination can still reduce illness severity, complications, and deaths
In summary, H3N2 is a significant seasonal flu subtype with potential for severe illness, and proactive measures—including vaccination and hygiene—are essential as Canada heads into the flu season.
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