Health officials are calling for people to ensure they are vaccinated against mpox, as there are indications the ‘clade Ib’ strain has spread locally in some European nations.

The UK Health Security Agency (UKHSA) says it is aware of small numbers of cases of this strain in Portugal, Spain, Italy and the Netherlands, as well as the US.

It says most of the new cases identified have been in gay, bisexual and other men who have sex with men, a population in which clade Ib mpox transmission has not previously been observed.

There are 16 clade Ib cases in the UK to date – all in England and unrelated to transmission within GBMSM (Gay, bisexual and other men-who-have-sex-with-men) community, a spokesperson for the agency 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,” said Dr Katy Sinka, head of sexually transmitted infections at UKHSA.

The UK has a routine mpox vaccination programme in place for eligible groups, including those who:

  • have multiple sexual partners
  • have group sex
  • visit sex-on-premises venues

Although there are no studies on vaccine effectiveness against clade Ib mpox, studies show that the vaccine is around 75 to 80% effective in protecting people against clade II.

The UKHSA said that since the last technical assessment on 19 December last year, the “probability of importation into the UK has increased from medium to high”.

The agency said, however, that the risk of onwards transmission in the UK is “likely to be controlled to some degree by the existing GBMSM vaccination programme and remains low to medium at present”.

Mpox is generally a mild infection, and clade Ib and la strains are no longer classified as a high-consequence infectious disease, but it can be severe in some cases, the UKHSA said.

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Charities have also called for people to get vaccinated prior to travelling to autumn Winter Pride events in Europe.

Common mpox symptoms include a skin rash or pus-filled lesions, which can last two to four weeks.

The infection can also cause fever, headaches, muscle aches, back pain, low energy and swollen lymph nodes.