UK health chiefs have sounded the alarm over a surge in mpox cases across Europe and the US.

The clade 1b mutation kills up to one in 100 of those infected and is believed to be behind a wave of miscarriages in Africa, where it emerged.

UK Health Security Agency (UKHSA) officials said it was aware of small numbers of cases of the strain in Spain, Italy, the Netherlands, Portugal and the US.

But none of the cases had a connection to countries with known clade 1b transmission, suggesting the rash-causing virus may be spreading undetected around the world.

Most of the cases identified have also been in gay and bisexual men, UKHSA officials said — which transmission of the strain hadn’t previously been observed in.

They have now urged all those eligible in the UK to get the mpox vaccine to thwart any potential spread of the virus across the country.

A different, less severe, form of mpox, called clade II, sparked alarm among health officials globally in 2022 when it began spreading rapidly across multiple countries mainly through sexual contact among gay and bisexual men.

However, new infections gradually tapered off amid boosted awareness of the disease and a hurried vaccination program.

At the time the UK reported almost 4,000 cases, with NHS England inoculating over 68,000 people against the disease with the smallpox vaccine, which works due to the two viruses being closely related.

Dr Katy Sinka, Head of Sexually Transmitted Infections at UKHSA, said: ‘The ways in which we are seeing mpox continue to spread globally is a reminder to come forward for the vaccine, if you are eligible.

‘Although mpox infection is mild for many, it can be severe.

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

‘It is important to remain alert to the risks from this unpleasant illness. Anyone who thinks they may have mpox should contact NHS 111 for advice on what to do.’

Chief executive of the Terrence Higgins Trust, Richard Angell, added: ‘The last outbreak of mpox hit the gay, bi and other men who have sex with men community disproportionately hard.

‘While it is described as “mild”, those who have the mpox rash around their face and body, including in intimate and sensitive areas, will tell you how unpleasant and painful it is.

‘In 2022, we were not prepared for the mpox outbreak and the tools available were hard to mobilise.

This time we have a government funded vaccine programme available to gay and bi men and it is strongly encouraged for those who have multiple partners, take part in sex parties and visit sex on premises venues.’

Clade 1b emerged last year and has swept mainly through central Africa infecting tens of thousands since the outbreak began.

Countries like the Democratic Republic of Congo have been hit especially hard with cases also spotted in Burundi, Rwanda, Uganda, and Kenya.

However, experts say fatality rates of clade 1b from central Africa are unlikely to be replicated in developed nations like the UK due to better access to higher quality healthcare.

Since October 2024, 16 cases of clade Ib have been reported in the UK, all in England.

All cases have had direct or indirect links to travel to countries where that strain is circulating.

Spain reported its first locally-acquired cases earlier this month, and another four cases were reported to the European Centre for Disease Prevention and Control (ECDC) among men in Italy, Portugal and the Netherlands.

All five had mild symptoms.

The ECDC says the cases had no travel history, which suggests ‘a different pattern of transmission’ and indicates ‘that transmission may be occurring in sexual networks among men who have sex with men in several EU/EEA countries’.

Following a surge in clade 1b cases last year, the World Health Organization (WHO) declared an ongoing mpox outbreak across several central African nations as a ‘public health emergency of international concern’.

This is the same designation the WHO gave Covid in late January 2020, just a few weeks before the virus ripped across the world.

Mpox causes characteristic lumpy lesions, as well as a fever, aches and pains and fatigue.

However, in a small number of cases, it can enter the blood and lungs, as well as other parts of the body, when it becomes life-threatening.

Current mpox vaccines, which are designed to work on smallpox a close relative of the mpox virus, were used during the 2022 outbreak against the milder strain.

But they have yet to be widely tested against the more potent clade 1b strain.

‘Although there are no studies on vaccine effectiveness against clade Ib mpox, vaccine protection is expected,’ the UKHSA said.

The WHO and the NHS recommends a vaccine within four days of contact with someone who has the virus or within up to 14 days if there are no symptoms.

Healthcare workers and men who have sex with men are advised to receive a vaccine even if they have had no mpox exposure.

There are no direct treatments available with medics focused instead on supporting a patient to help their body fight off the virus.