AMMI Canada issues 2025-2026 seasonal influenza guideline update

The Association of Medical Microbiology and Infectious Disease Canada (AMMI Canada) has summarized key considerations about influenza and antiviral use for the 2025-26 season. In preparing the update, AMMI Canada focused on three crucial questions:1. What stands out for the 2025-26 season and why is the vaccine still recommended?A substantially mutated (antigenically drifted, vaccine mismatched) variant of influenza A(H3N2) termed subclade K triggered an unusually early and intense start to the 2025–26 season in several countries of the Northern Hemisphere. A sharp rise in A(H3N2) subclade K infections occurred in Canada, beginning with children. Children often experience the highest influenza attack rates early in the season before spreading to other age groups.1Influenza test positivity has been highest among individuals aged 5–19 years, but adults age ≥ 65 years have experienced the highest hospitalization rates. Seasons in which A(H3N2) dominates are typically associated with greater severity overall, including more hospitalizations and deaths especially among older adults.1The 2025–26 influenza vaccines available in Canada are trivalent. Considering the major genetic and antigenic differences between circulating subclade K viruses relative to the chosen A(H3N2) component of the 2025–26 vaccine strain, lower vaccine effectiveness is anticipated, but the actual degree of vaccine protection against subclade K awaits evaluation. Some degree of cross-protection is expected. Early estimates from the United Kingdom show promise for protection against severe outcomes. Interim Canadian estimates are expected in early 2026.1 In the meantime, influenza vaccination remains important and highly recommended. Since influenza A epidemics are often followed by influenza B activity later in the season, it is not too late to benefit from vaccination. Preventing serious respiratory infections through immunization also helps to prevent outbreaks in care settings and lessen strain across the healthcare system.12. Which antiviral medications are available in Canada in 2025–26 and what is advised for children and adults?New since the previous (2023) AMMI Canada influenza update2 is access to baloxavir, an antiviral first authorized in 2020 but not brought to market in Canada until 2025. The role for this new antiviral medication currently remains limited overall in the Canadian context. This is in part due to lack of study for protection against severe disease and concerns about the emergence of antiviral resistance, compounded by cost and accessibility issues (it may not be readily available in all settings).1 The 2025–26 AMMI Canada update includes a quick reference table summarizing current antiviral medications in Canada. The table compares oseltamivir, zanamivir and baloxavir in terms of route of administration, dosages forms, drug class, availability considerations, approximate cost per treatment course, approved indications, comparative considerations, viral resistance considerations, most common adverse effects, administration considerations, use in pregnancy/lactation, usual treatment dose, renal/hepatic adjustment, precautions/interactions and additional considerations. All antiviral therapies have shown greatest benefit when given early in the course of illness, ideally within 48 hours of symptom onset.1A second table summarizes antiviral treatment considerations for influenza illness in children, with sample case scenarios. The text of the article also includes a discussion of management of children with antivirals.1 3. Are any changes recommended in the way antiviral medications are used for the 2025–2026 season?Healthcare providers may ask how to optimally manage care for severely ill patients, during a more severe influenza season. However, no changes to treatment are currently recommended. In severely ill patients, higher doses of oseltamivir have not been shown to be any more effective than standard dosing. Therefore, increasing the dose of neuraminidase inhibitors (oseltamivir, zanamivir) is not advised.1Some immunocompromised individuals with severe illness may have significant prolonged viral replication along with sustained or periodic influenza-like illness exacerbations despite a complete course(s) of antiviral therapy. Extending the duration of treatment with neuraminidase inhibitors (e.g., oseltamivir) to 10 days in this patient population may be reasonable. Prolonged shedding with severe influenza despite antiviral therapy should prompt a request for antiviral resistance testing by consulting the local diagnostic or public health laboratory.1Currently, AMMI Canada has not issued any recommendations for combination antiviral therapy. The clinical value of combination therapy for treating influenza remains uncertain and results from observational studies have been mixed. A randomized controlled trial combining baloxavir with a neuraminidase inhibitor did not result in superior clinical outcomes compared with a neuraminidase inhibitor alone. However, as novel influenza virus infections in humans emerge, with concern about antiviral resistance, further research will address this issue.1SummaryPrimary prevention of influenza through immunization plus early use of antiviral therapies should ease the burden for ill patients with high-risk conditions, or those who are hospitalized due to severe disease.1References:Harrison R, Reid EK, Allen UD, et al. AMMI Canada seasonal influenza guideline update 2025-26: some questions answered. JAMMI 2026; published online January 16, 2026. (accessed January 22, 2026).Harrison R, Mubareka S, Papenburg J, et al. AMMI Canada 2023 update on influenza: management and emerging issues. J Assoc Med Microbiol Infect Dis Can 2023;8(3):176-85. (accessed January 22, 2026).

AMMI Canada issues 2025-2026 seasonal influenza guideline update

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