- Seasonal influenza is surging earlier than expected this winter, driven by the highly contagious H3N2 subclade K.
- Greece reports sharp increases in cases and hospitalizations.
- The strain spreads more easily due to new mutations, but there is no evidence of higher mortality.
- Older adults, children, pregnant women, and people with chronic conditions face a higher risk of severe illness.
- This season’s flu vaccine is not a perfect match, though it still helps reduce severe outcomes.
Travel Advisory
- Winter travelers should be aware that airports, ferries, cruise ships, public transport, and indoor attractions increase the risk of exposure.
- Visitors who feel unwell should avoid travel while symptomatic, seek medical advice promptly, and allow extra recovery time in their itineraries.
- Individuals in vulnerable groups should take additional precautions, particularly when traveling during peak holiday and winter periods.
Seasonal influenza is arriving earlier and spreading faster than usual this year, according to microbiology professor Athanasios Tsakris, as a highly transmissible H3N2 strain is driving a sharp rise in cases across Greece.
Each winter, influenza outbreaks are primarily caused by three variants: influenza A subtypes H1N1 and H3N2 and influenza B. While H1N1 and H3N2 often co-circulate, one typically predominates. This season, an H3N2 strain known as subclade K has taken hold, triggering a major epidemic wave three to four weeks earlier than expected.
Why This Flu Season Is Different
According to Professor Tsakris, director of the Microbiology Laboratory at the National and Kapodistrian University of Athens Medical School and president of the Scientific Council of the Hellenic Foundation for Research and Innovation (ELIDEK), subclade K is more transmissible because of its genetic diversity.
Compared with earlier H3N2 strains, it carries ten new mutations in the hemagglutinin gene, which helps the virus attach to human cells. These mutations reduce the immune system’s ability to recognize the virus, even in people previously exposed to similar strains.
This has contributed to earlier outbreaks, more intense transmission, and increased hospitalizations. Importantly, there is currently no evidence that the strain causes more severe disease or higher mortality than previous H3N2 variants.
Who Is Most at Risk
H3N2 infections are typically more severe in vulnerable groups. While about 90 percent of reported cases involve people under 59, most hospitalizations occur among adults over 69 and children under 14. Infants, young children, pregnant women, and people with chronic conditions are also considered higher-risk.
This year’s flu vaccine was developed before subclade K became dominant, meaning the match is not exact. Health experts nonetheless emphasize that vaccination remains important because it continues to protect against severe illness and complications.
