European health officials are sounding teh alarm about an early and potentially severe influenza season, with cases rising three to four weeks ahead of recent years. the surge is being driven by a newly identified variant of the H3N2 virus, dubbed A(H3N2) K, wich exhibits meaningful differences from strains used in current vaccines. The European center for Disease Prevention and Control is urging eligible individuals to get vaccinated immediately, citing concerns about increased healthcare strain and the potential for a challenging winter season.
Influenza activity is rising earlier than usual across Europe, with the season starting three to four weeks ahead of the past two years. A newly circulating variant, a subtype of H3N2 known as A(H3N2) K, is driving this increase, according to a risk assessment released today by the European Centre for Disease Prevention and Control.
Flu cases are increasing unusually early across the European Union/European Economic Area (EU/EEA) compared to recent years, starting three to four weeks ahead of the previous two seasons. The rise is being fueled by a new viral variant: the A(H3N2) K subclade, according to a threat assessment published November 20, 2025, by the European Centre for Disease Prevention and Control (ECDC). The agency is urging individuals who are eligible to receive a flu vaccine to get vaccinated without delay. This early surge in influenza activity highlights the importance of preventative measures as the winter season approaches.
Call for Vaccination
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“We are observing an increase in influenza detections much earlier than usual this year, and that means time is of the essence,” said Edoardo Colzani, head of respiratory viruses at the ECDC. “If you are eligible for vaccination, please don’t wait. Getting vaccinated now is one of the most effective ways to protect yourself and those around you from severe illness during the winter.”
While uncertainty remains regarding the public health impact of the upcoming flu season, the ECDC is preparing for a scenario in which Europe could face a more severe season than in the past, particularly if vaccination rates are low. A higher-than-normal number of infections would also put additional strain on healthcare systems.
ECDC Recommendations
- Individuals at highest risk of severe illness should get vaccinated without delay. These groups include those over 65, pregnant women, people with chronic illnesses or conditions that compromise the immune system, and those living in congregate settings like long-term care facilities.
- Vaccinate if you work in healthcare or a long-term care facility.
- Healthcare facilities and long-term care facilities should strengthen their preparedness plans and infection prevention and control measures, and encourage staff and visitors to wear masks during periods of increased circulation of respiratory viruses.
- Healthcare professionals should consider timely administration of antivirals to patients at high risk of severe illness to reduce complications.
- Healthcare professionals should consider the use of antiviral prophylaxis during outbreaks in closed settings, such as long-term care facilities.
- Countries should promote clear and targeted communication on vaccination, hand hygiene, and respiratory etiquette to help reduce transmission in the community.
Influenza Numbers
Circulating respiratory viruses, including influenza viruses, SARS-CoV-2, and RSV, all contribute to pressure on healthcare systems during winter in the EU/EEA. In a typical season, influenza causes substantial morbidity in the European population, with up to 50 million symptomatic cases and 15,000 to 70,000 deaths annually. All age groups are affected, although children have higher rates of illness and are usually the first to get sick and transmit the disease within families, which can promote transmission in the community. It is estimated that up to 20% of the population contracts influenza each year. This translates to absences from school and work and a significant impact on healthcare systems. A greater impact is observed in closed environments such as long-term care facilities, where seasonal influenza epidemics can have high morbidity and mortality.
Threat Assessment
The ECDC has assessed the risk of influenza for the EU/EEA in the context of the early circulation of seasonal influenza in the region and the recently emerged and globally circulating A(H3N2) K subclade. The goal is to raise public awareness of potential implications and provide recommendations to public health authorities. However, considerable uncertainty remains about the likely public health impact of this subclade on the influenza season. A detailed threat assessment is available from the ECDC.
Compared to previous years, influenza is increasing unusually early in the EU/EEA, with the A(H3N2) virus driving the increases in recent weeks. This situation reflects developments recently reported from other countries in the Northern Hemisphere. The newly identified A(H3N2) K subclade (formerly J.2.4.1) has been detected on all continents and accounts for one-third of all A(H3N2) sequences deposited in the Global Initiative on Sharing All Influenza Data (GISAID) between May and November 2025 globally, and nearly half in the EU/EEA. Phylogenetic analysis shows significant divergence of the K subclade from the Northern Hemisphere A(H3N2) vaccine strain. In vitro antigenic and serological analyses also suggest a mismatch between the vaccine and this new subclade. Real-world vaccine effectiveness data are currently limited.
A(H3N2) has not been the dominant virus in recent seasons, which could lead to a reduction in immunity in populations without recent exposure, although serological data are not yet available for a more thorough assessment. Countries in East Asia that are now reporting a decline in A(H3N2) epidemics have not experienced unusually high disease severity, and phylogenetic analysis suggests that the A(H3N2) K subclade strains circulating in these countries are not different from those present in the EU/EEA. Even if A(H3N2) prevails this winter, the vaccine is still expected to provide protection against severe illness, remaining a crucial tool for public health.
