UKHSA announces UK’s first cases of Clade lb mpox

Government is working with UKHSA and NHS to prevent transmission, including securing vaccines and giving healthcare professionals the necessary tools

The UK Health Security Agency (UKHSA) has reported the first detected cases of Clade Ib mpox in the UK. It is a new strain which is fuelling a surge in infections in Africa. 

The first person to test positive developed flu-like symptoms after returning to London in late October, having recently travelled to countries in Africa that are seeing community cases of Clade Ib mpox. In early November, three additional cases were confirmed. All patients live in the same household.

They are the first locally transmitted clade Ib mpox cases in the WHO European Region, and the first outside Africa since a Public Health Emergency of International Concern was declared for a second time in August 2024. 

Dr Hans Henri P. Kluge, WHO Regional Director for Europe said, “The overall risk to the general population in the United Kingdom and wider Region remains low, but local transmission of clade Ib mpox should be the impetus for health systems across our Region to heighten their surveillance measures and prepare for rapid contact tracing of suspected and confirmed cases.” 

While the existing evidence suggests mpox Clade Ib causes more severe disease than Clade II, UKHSA says it will continue to monitor and learn more about the severity, transmission and control measures. 

Wes Streeting, Health and Social Care Secretary said the government is working alongside UKHSA and the NHS to protect the public and prevent transmission. “This includes securing vaccines and equipping healthcare professionals with the guidance and tools they need to respond to cases safely. We are also working with our international partners to support affected countries to prevent further outbreaks.”

Clade Ib mpox has been widely circulating in the Democratic Republic of Congo (DRC) in recent months and there have been cases reported in Burundi, Rwanda, Uganda, Kenya, Sweden, India and Germany.

The new strain was detected by UKHSA using polymerase chain reaction (PCR) testing.

Common symptoms of mpox include a skin rash or pus-filled lesions which can last two to four weeks. It can also cause fever, headaches, muscle aches, back pain, low energy and swollen lymph nodes.

The infection can be passed on through close person-to-person contact with someone who has the infection or with infected animals and through contact with contaminated materials.

“Vaccination remains the best strategy to prevent mpox and is recommended to individuals at higher risk of infection…”

Dr Jonas Albarnaz, Institute Fellow, The Pirbright Institute said, “Vaccination remains the best strategy to prevent mpox and is recommended to individuals at higher risk of infection, which include contacts of mpox cases, healthcare workers, and people with multiple sexual partners. 

“Two vaccines are approved against mpox: MVA-BN and LC16,” added Dr Albanaz. “These vaccines are based on weakened versions of a related orthopoxvirus (vaccinia) and were developed against smallpox (now eradicated).  However, availability of these vaccines is very limited, representing a major bottleneck for the control strategies.”

The UK has an existing stock of mpox vaccines and further vaccines are being procured to support a routine immunisation programme.