Mpox UK: difference between Clade 1 and Clade 2 strains explained as first case detected outside of London

• The first case of new mpox variant has been found outside of London.
• There are four variants of the virus, Clade 1a, 1b and Clade 2a and 2b.
• In August, the World Health Organization (WHO) declared a global health emergency following an outbreak of mpox in Africa.
• The latest case was detected in Leeds and is unrelated to the London outbreak.

The first case of the new mpox variant has been found outside of London the UK Health and Security Agency (UKHSA) have confirmed.

Discovered in Leeds, this case is unrelated to the outbreak in London, with all previous mpox cases being from the same household.

Clade Ib mpox has been widely circulating in the Democratic Republic of Congo (DRC), Burundi, Rwanda, Uganda and Kenya in recent months, leading to the WHO declaring a global health emergency in August. Cases have also been detected in Canada, Sweden, India, Thailand and Germany.

There are many different types of variants of mpox, known as Clades, with the current outbreak being driven by Clade 1b, here is everything you need to know about the differences between strains.

How many cases of mpox are there in the UK?

There are now five confirmed cases of mpox in the UK reported by the UKHSA, with the fifth reported in Leeds on November 29. The first four cases which came from the same household were detected in London, with the initial infection coming from someone who had recently travelled to countries in Africa that are seeing community cases of Clade 1b.

The case in Leeds is unrelated to the London outbreak, the patient had recently returned from Uganda and is now under specialist care at Sheffield Teaching Hospitals NHS Foundation Trust.

The threat to the public is still described as “low”. Professor Susan Hopkins, Chief Medical Adviser at UKHSA, said: “It is thanks to clinicians rapidly recognising the symptoms and our diagnostics tests that we have been able to detect this new case.”

Professor Hopkins continued: “The risk to the UK population remains low following this fifth case, and we are working rapidly to trace close contacts and reduce the risk of any potential spread. In accordance with established protocols, investigations are underway to learn how the individual acquired the infection and to assess whether there are any further associated cases.”

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What is the difference between Clade 1 and Clade 2?

There are four different variants of mpox, Clade 1a, 1b and Clade 2a and 2b. Speaking about mpox in August, Professor Paul Hunter, Professor in Medicine at the University of East Anglia explained that Clade 1a and 2a are “almost entirely acquired from contact with animals and usually primarily affects children”.

Whilst Clade b, which is the variant that experts are concerned about about, originated in animals but “now is spreading person to person through sexual and intimate contact.”

Clade 2b has been in the UK since the last global outbreak in 2022, with nearly 4,000 cases detected since May 2022. Cases of Clade 2 are normally mild, with Clade 1 being more serious and potentially life-threatening, with 582 confirmed deaths in the Democratic Republic of Congo (DRC).

Clade 1 is incredibly rare in the UK, with only five cases of the Clade 1b variant detected so far.

What are the symptoms of mpox?

The first symptoms of mpox are flu-like, according to the NHS this can include a fever, headache, muscle aches, backache, chills or exhaustion. A rash then follows one to five days after after your initial symptoms which can appear on the face, before spreading to other areas of the body including the mouth, genitals and anus.

Is there a vaccine?

There is a vaccine for mpox available on the NHS for those who are at higher risk of being exposed to the virus.

Those who could be offered the vaccine include gay, bisexual, or other men who have sex with men who have previously identified as being higher risk, certain healthcare workers, certain healthcare specialist and humanitarian workers who go to affected countries and close contacts of a confirmed case.

In a statement from the UKHSA Professor Hopkins said: “Alongside vaccination, we have been working rapidly to ensure that clinicians are aware and able to recognise cases promptly, that rapid testing is available, and that protocols are developed for the safe clinical care of people who have the infection and the prevention of onward transmission.”

You can find out more about the signs and symptoms of mpox and who is eligible for the vaccine at NHS.UK.