A new strain of smallpox, formerly called monkeypox, has been discovered in a person in England, UK health officials said.
The virus is a mixture of two main types of virus, the MPox virus, and was discovered in a person who had recently returned from traveling in Asia.
Officials say they are still assessing the significance of the new strain.
The UK Health Security Agency (UKHSA) says it is normal for viruses to evolve. Vaccination remains the best way to protect against severe disease, although for many people Mpoxoma infection is mild.
The new virus strain contains elements of two mpox strains, called clade Ib and clade IIb. It currently has no name.
The call comes after a strain called clade Ib showed early signs of local spread in some European countries.
“Clade IIb” is associated with the global mpox outbreak in 2022, which affected many countries around the world.
In the UK, vaccination is available to the groups of people at highest risk of contracting smallpox:
- those who have multiple sexual partners
- those who have group sex
- those who visit sex establishments on the territory
Health officials say the vaccine is 75 to 80% effective in protecting against mpox.
There have been no studies on how well the vaccine protects against this latest strain, although protection is expected to be high.
Dr Kathy Sinka, head of sexually transmitted infections at the UKHSA, said genomic testing enabled its detection.
“Virus evolution is normal, and further analysis will help us better understand how mpox changes.
“Vaccination is a proven, effective way to protect yourself from serious illness, so please be sure to get vaccinated if you are eligible,” she said.
Professor Trudy Lang, director of the Global Health Network at the University of Oxford, said the UK has “excellent systems” for identifying cases and controlling the spread of infection, but in other parts of the world, among more vulnerable populations, “this is harder to achieve” where access to vaccines is less reliable.
Professor Lang said if new cases of the strain emerge in the UK and other countries, it will be important to understand how it spreads and how sick it makes people to assess whether it is more or less dangerous than previous strains.
There have been about 48,000 confirmed cases of MPox virus worldwide in 2025, and 2,500 in the past month, with the majority occurring in central Africa.
Dr. Boguma Titanji, an assistant professor of medicine at Emory University, said the new strain is what experts feared would happen if mpox continued to spread around the world.
“The more circulation of MPox we allow, the more opportunities the virus will have to recombine and adapt, further cementing MPox as a human pathogen that is here to stay,” she said.
Mpox can be a nasty disease.
Common symptoms include lesions or skin rashes that can last two to four weeks, as well as fever, headaches, back pain, muscle aches and fatigue.
The virus is spread from person to person through close physical contact, coughing or sneezing, or touching contaminated clothing, bedding, or towels.
Health officials say anyone who thinks they may have MPO should contact NHS 111 for advice on what to do.
