Archive · 9 Dec 2025
UK Faces Surge in 'K' Strain Super-Flu
There's a new type of flu called the 'K' strain that's spreading quickly in the UK.
It's part of the H3N2 family, which usually causes more severe illness.
This new strain has changed a bit, so the vaccine might not protect as well as before.
Even though it's not more dangerous than other H3N2 strains, more people are getting sick because fewer have been exposed to flu in recent years.
Doctors are advising everyone to get the flu vaccine to stay safe.
The 'K' strain of the H3N2 flu virus is causing a significant surge in cases in the UK, with hospital admissions up 50% compared to last year.
This strain has undergone genetic drift, making it different from the strain used in this season's flu vaccine, potentially reducing its effectiveness.
While the 'K' strain is not more virulent, H3N2 generally causes more severe illness and is more infectious than other flu strains.
Factors contributing to the rise in cases include an earlier start to the flu season and lower immunity due to fewer recent exposures.
Health officials are encouraging everyone eligible to get the flu vaccine, which is still considered the best defense against the virus.
- Who
- General public, especially children and eligible individuals in the UK
- What
- Surge in cases of the 'K' strain of the H3N2 flu virus
- When
- Current flu season, starting earlier than usual
- Where
- Primarily in the UK, with similar trends in Japan, and possibly the US and Canada
- Why
- The 'K' strain has undergone genetic drift, making it different from previous strains and the vaccine, and fewer people have built up immunity
- Virus Type
- Influenza A H3N2 (Subclade K)
- Severity
- Not more virulent than other H3N2 strains
- Vaccine Effectiveness
- 70-75% in children, 30-40% in adults
- Hospital Admissions
- 50% higher than last year, 10 times higher than 2023
- Predominant Regions
- UK, Japan, and possibly US and Canada