A new strain of mpox, previously called monkeypox, has been detected in a person in England, say UK health officials.

The virus is a mix of two major types of the mpox virus, and was found in someone who recently returned from travelling 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. Getting vaccinated remains the best way to protect against severe disease – although an mpox infection is mild for many.

The new virus strain contains elements of two mpox strains, called clade Ib and clade IIb.

UK health officials recently encouraged gay, bisexual and other men who have sex with men to make sure they were vaccinated against mpox.

That call came as a strain called ‘clade Ib’ showed early signs of local spread in some European countries.

Clade IIb is linked to a global outbreak of mpox in 2022 which affected many countries worldwide.

In the UK, vaccination is available for groups of people at highest risk of catching mpox:

• those who have multiple sexual partners
• those who engage in group sex
• those who visit sex-on-premises venues

Health officials say the vaccine is 75-80% effective at protecting against mpox.

But those studies were in people with one type of mpox, called clade II. There have been no studies on how well the vaccine protects against another type called clade Ib, although it’s thought there will be a high degree of protection.

Dr Katy Sinka, head of sexually transmitted infections at UKHSA, said genomic testing had allowed detection of the new strain.

“It’s normal for viruses to evolve, and further analysis will help us understand more about how mpox is changing.

“Getting vaccinated is a proven effective way to protect yourself against severe disease, so please make sure to get the jab if you are eligible,” she said.

Prof Trudie Lang, director of the Global Health Network at the University of Oxford, said this case of a new mpox virus “highlights that mpox is circulating globally and is evolving”.

She said in the UK there were “excellent systems” to identify cases and control onward infection, but in other parts of the world, in more vulnerable populations, “this is harder to achieve”, where access to vaccines is not as reliable.

Prof Lang said if further cases of this strain appeared in the UK and elsewhere, it would be important to understand how it’s being spread in order to assess whether it’s more or less dangerous than previous strains.

Mpox can be a unpleasant illness.

Common symptoms are lesions or a skin rash, which can last for two to four weeks, plus fever, headaches, back pain, muscle aches and tiredness.

The virus spreads from person to person through close physical contact, coughs or sneezes and touching infected clothing, bedding or towels.

Health officials say anyone who thinks they might have mpox, should contact NHS 111 for advice on what to do.