The UK has ordered more than 150,000 doses of vaccine against mpox to bolster its preparedness after the World Health Organization declared a surge in cases in Africa to be a global emergency.

No cases of clade Ib mpox, the new strain that has spread rapidly in Africa after an initial outbreak in the Democratic Republic of the Congo (DRC), have yet been detected in the UK.

However, UK health officials said at a briefing on Monday that ordering more vaccine was necessary to bolster the country’s resilience against the virus, formerly known as monkeypox.

They also set out three scenarios illustrating the possible impact of a UK outbreak.

The first involved small clusters of cases, the second a “controllable epidemic” and the third community transmission in hospitals, care homes, prisons and schools. None of the scenarios outlined were projections or predictions, officials said.

“We are preparing for any cases that we might see in the UK and vaccination plays a vital part in our defences,” said Susan Hopkins, the chief medical adviser at the UK Health Security Agency.

“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.”

Mpox is passed on through close physical contact. The disease causes flu-like symptoms and pus-filled lesions, and is usually mild but can kill. Children, pregnant women and people with weakened immune systems are at higher risk of complications.

The vaccine, made by Bavarian Nordic, would be offered to those eligible in stages, and based on clinical need, health officials said.

Gay, bisexual, or other men who have sex with men; certain healthcare workers and specialist healthcare and humanitarian workers who go to affected countries; and close contacts of confirmed mpox cases would be offered vaccines, officials said.

Clade Ib has prompted more concern among health officials than clade IIb, which was responsible for a global outbreak of the virus in 2022. Small numbers of cases of clade IIb have been present in the UK for about two years.

A vaccination programme was launched in the summer of 2022 and closed in the summer of 2023. It is understood that about 50,000 people have had two doses of the jab, which is 80% effective at preventing mpox cases, while more than 83,000 have had one dose.

Steve Russell, NHS England’s director for vaccinations and screening, said that while the risk of catching mpox in the UK was low, vaccination offered “a vital level of protection” for those most likely to be exposed.

“We encourage those eligible to come forward when invited by local health services, to ensure they have the best defence,” he added.

The health secretary, Wes Streeting, said he was closely monitoring the spread of mpox overseas.

He added: “No cases of clade Ib mpox have been detected in the UK, but we are taking steps to ensure the country is prepared with a robust vaccination programme that protects those who may be at high risk.”