This brings the total number of confirmed cases of Clade lb mpox strain in the country to three.
The UKHSA said the risk to the UK population “remains low” and that the two patients are currently in specialist care at Guy’s and St Thomas’ NHS Foundation Trust in London.
The country’s first case was discovered in London last week in a man who had been on holiday in Africa and returned to the UK on an overnight flight on 21 October.
They developed flu-like symptoms more than 24 hours later and on October 24 began developing a rash that worsened over the following days.
The contacts of all three cases are being traced by UKHSA and other partner organizations and will be offered tests, vaccinations and advice if necessary.
Professor Susan Hopkins, Chief Medical Adviser at UKHSA, said: “Mpox is highly contagious in households with close contact and so it is not unexpected to see additional cases in the same household.
“The overall risk to the UK population remains low.
“We are working with partners to ensure all contacts of the cases are identified and contacted to reduce the risk of further spread.”
Mpox is spread between people only through direct contact with a rash, skin lesions, or scabs caused by the virus, including during sex, kissing, cuddling, or other skin-to-skin contact.
There is also a risk of contact with body fluids such as saliva or snot; contact with bedding or towels or clothing; and the ability to spread through close and prolonged face-to-face contact, such as talking, breathing, coughing or sneezing.
Symptoms include a skin rash with blisters, spots or sores that can appear anywhere on the body, fever, headache, back pain and muscle aches.
The rash usually appears one to five days after fever, headache, and other symptoms.
Clade Ib mpox has been widespread in the Democratic Republic of the Congo (DRC) in recent months, and cases have been reported in Burundi, Rwanda, Uganda, Kenya, Sweden, India and Germany.
A report by the World Health Organization (WHO) and the African Centers for Disease Control and Prevention said there were more than 40,000 mpox cases linked to almost 1,000 deaths in Africa by the end of September 2024, with clades Ia, Ib and II circulating in the region.
The WHO has declared a public health emergency of international concern due to the rapid spread of the mpox strain.
Health and Social Care Secretary Wes Streeting said last week the Government was working with UKHSA and the NHS “to protect the public and prevent transmission”.
“This includes providing vaccines and equipping health professionals with the guidance and tools they need to safely respond to cases,” he added.
“We are also working with our international partners to support affected countries to prevent further outbreaks.”