UK health authorities have identified a previously unknown strain of mpox — formerly called monkeypox — in a person returning from Asia. The virus appears to be a combination of two major mpox lineages, known as clade Ib and clade IIb, though the new strain has not yet been formally named.
The UK Health Security Agency (UKHSA) said that viral evolution is normal and that vaccination remains the most effective protection against severe disease. While many mpox infections are mild, vaccination is strongly recommended for those at higher risk, particularly gay, bisexual and other men who have sex with men.
Groups eligible for vaccination include those with multiple sexual partners, individuals who engage in group sex, and visitors to sex-on-premises venues. The vaccine is estimated to be 75–80% effective against mpox, though its efficacy against the new strain is still being assessed.
Dr Katy Sinka, head of sexually transmitted infections at UKHSA, explained that genomic testing allowed the new strain to be detected. “It’s normal for viruses to evolve, and further analysis will help us understand how mpox is changing. Getting vaccinated remains a proven way to protect yourself against severe disease,” she said.
Prof Trudie Lang, director of the Global Health Network at the University of Oxford, highlighted that while the UK has “excellent systems” to identify and control infections, other countries with more vulnerable populations face greater challenges due to limited vaccine access. She added that monitoring how the strain spreads and its severity will be crucial to determining whether it is more or less dangerous than existing variants.
Globally, nearly 48,000 mpox cases have been confirmed in 2025, with around 2,500 reported in the past month, mostly in central Africa. Dr Boghuma Titanji, assistant professor of medicine at Emory University, warned that continued global transmission increases the virus’s opportunity to recombine and adapt, potentially cementing mpox as an enduring human pathogen.
Mpox typically causes a skin rash or lesions lasting two to four weeks, along with fever, headaches, back pain, muscle aches and fatigue. The virus spreads through close physical contact, respiratory droplets, and contaminated clothing, bedding or towels.
Health officials advise anyone who suspects they may have mpox to contact NHS 111 for guidance on testing and care.
