A/H3N2 Flu Variant Drives 90% of Recent Cases
As the flu season begins, the A/H3N2 variant is driving a significant increase in cases across the globe. This year, flu activity has surged earlier than expected, with reports indicating that nearly 90% of flu cases in the United Kingdom and Japan are attributed to the A/H3N2 subclade K.
A/H3N2 Flu Variant Overview
Flu viruses primarily belong to two types: influenza A and influenza B. Among them, A/H3N2 has emerged as a major concern this season. The A/H3N2 subclade K was observed to be 90% of the flu cases analyzed between May and November 2025 in various countries.
Global and Regional Trends
- United Kingdom and Japan: Nearly 90% of flu samples are A/H3N2 K.
- United States and Canada: Following similar trends with increasing A/H3N2 cases.
- European Union: A/H3N2 accounted for nearly half the flu cases analyzed.
- Japan: Recorded an unusually high number of cases since October.
- Spain: Exceeded the epidemic threshold earlier than anticipated.
Characteristics of A/H3N2 Subclade K
The A/H3N2 subclade K is not fundamentally different from previous strains but exhibits some genetic mutations. These changes do not come from virus mixing and do not significantly impact the severity of outcomes or treatment efficacy.
- Subclade K mutations are expected as the virus evolves to evade immunity.
- Current data indicates that these strains do not differ significantly from those circulating in Europe.
Implications for Public Health
Despite the prevalence of A/H3N2 K, there is no evidence to suggest that it causes more severe illness. However, health experts highlight a potential increase in flu cases this season due to lower population immunity resulting from reduced recent exposure.
Flu Symptoms
Common symptoms associated with the flu include:
- Sudden high temperature
- Aching body
- Fatigue
- Dry cough
- Sore throat
- Headache
- Loss of appetite
Vaccine Effectiveness
This year’s flu vaccine has been formulated to combat two subtypes of A/H1N1, influenza B, and an earlier type of A/H3N2. There are concerns regarding the effectiveness of the vaccine against the new A/H3N2 subclade K, but any vaccination still offers some level of protection.
- Vaccines remain crucial for preventing severe illness, especially for vulnerable groups.
- Health authorities recommend vaccination as early as possible due to the season’s early start.
Recommendations
For optimal protection, it is advisable to get vaccinated promptly. Additionally, practicing good hygiene, such as handwashing and mask-wearing, is essential in minimizing the spread of infection.
Though the A/H3N2 subclade K does not appear to be more virulent, the early arrival of the flu season and its current prevalence may lead to increased hospitalizations and demand for healthcare services.
