Flu Season 2026: Vaccination and Rising Cases of Influenza A(H3N2)

As autumn arrives and virus circulation increases, influenza, commonly known as the flu, is once again a significant concern for public health. This respiratory infection can range from mild symptoms like fever and cough to severe complications. The World Health Organization (WHO) estimates that influenza causes approximately 3 to 5 million serious cases and up to 650,000 respiratory-related deaths annually [1]. Vaccination and epidemiological surveillance are crucial tools for protecting vulnerable populations and mitigating the impact of the flu each season.

Rising Influenza Activity and the A(H3N2) Subclade

Recent data indicates a rising trend in influenza activity across the Americas. According to the National Epidemiological Bulletin N°797, published on March 2, 2026 (epidemiological week 7, February 14-21, 2026), the region is experiencing a predominance of the A(H3N2) virus, with 28.2% of tests coming back positive for influenza [1]. Argentina has reported 45,485 cases of Influenza-like Illness (ILI) in the first six weeks of 2026, defined as acute respiratory infection with fever of 38°C or higher, cough, and symptom onset within 10 days [1].

A specific subclade, K, of the influenza A virus subtype H3N2 has been identified and is associated with a higher rate of hospitalizations. This is due to the influenza virus’s constant evolution, leading to variations that can increase its transmissibility or severity [1]. Genetic analysis has identified 76 cases of the K subclade of A(H3N2) in 19 jurisdictions, affecting both outpatient and inpatient cases. The majority of these cases are occurring in individuals under 10 years old and over 60 years old.

Who is at Risk?

The influenza virus primarily spreads through respiratory droplets produced when coughing, sneezing, or talking, and through contact with contaminated surfaces [1]. The incubation period is typically one to four days, with symptoms lasting about a week, although coughs can persist longer. Risk groups include:

• Pregnant women
• Children under five years of age
• Individuals over 65
• People with chronic diseases or immunosuppression

In older adults, influenza may not always present with a fever but can lead to complications like bacterial pneumonia or worsening of existing chronic conditions.

Vaccination: Your Best Defense

Annual vaccination remains the most important measure to prevent influenza, particularly for high-risk groups [1]. The WHO recommends vaccination for healthcare workers to protect themselves and vulnerable patients [1]. Vaccination is recommended for children between 6 and 24 months, adults 65 years and older, pregnant women, individuals with chronic diseases, those with morbid obesity, people with immunosuppression, healthcare personnel, and those living with vulnerable patients. Children 6 months to 8 years old without prior vaccination require two doses, separated by at least four weeks.

Most flu vaccines available in Argentina this year protect against three types of influenza viruses. Some vaccines are specifically designed for older adults, containing adjuvants to enhance the immune response or a higher dose of antigen. Vaccines manufactured using cell-based or protein-based technologies are similarly available, offering equivalent protection. Vaccines are widely accessible in authorized centers, often without requiring prior appointments, and some providers offer home vaccination services.

This year’s vaccination campaign includes protection against the K variant of the A(H3N2) virus. Vaccines are expected to be available from late February through early winter.

Beyond Vaccination: Preventative Measures

In addition to vaccination, public health authorities recommend the following preventative measures:

• Frequent hand washing
• Ventilation of indoor environments
• Covering coughs and sneezes with the bend of the elbow
• Regular cleaning of surfaces

Strengthening epidemiological surveillance and reporting positive samples are also crucial for early identification of variants and adapting prevention strategies.

Looking Ahead

Continued surveillance, vaccine updates, and widespread vaccination efforts are essential to minimize the impact of influenza. The WHO provides Member States with strategic guidance and technical support to enhance preparedness against seasonal, zoonotic, and pandemic influenza threats [3]. The WHO also issues recommendations on the composition of influenza vaccines twice a year, guiding vaccine development and production [3]. For the 2026-2027 northern hemisphere influenza season, the WHO recommends an A/Missouri/11/2025 vaccine component [3].