Mpox

Mpox, previously called ‘monkeypox’, is a rare disease caused by an infection from the monkeypox virus. The virus is an orthopox virus and causes similar symptoms to smallpox, although less severe.

The virus was originally found in captive research monkeys in Denmark in 1958, before being found in humans in 1970 in north-eastern Equateur province of the Democratic Republic of Congo (DRC), in Central Africa.

Since then, there have been sporadic outbreaks. Cases have been most commonly found in East, West, or Central Africa, according to the World Health Organization (WHO). 

There are two types (clades) of the virus, which each have sub-types. Clade I has been responsible for outbreaks mainly in Central and East Africa, while clade II has been found more commonly in West Africa.

Clade II was responsible for a global outbreak that started in 2022, which is still on-going, although case numbers are now significantly lower.

The recent emergence of a new sub-type – clade Ib – in the DRC is worrying public health experts, as it appears to cause more severe disease and more deaths. By the end of August, clade I cases had been reported in nine countries, either bordering or close to the DRC. A further couple of cases have been found in Sweden and Thailand.

In all, between January 2022 and 31 July 2024, there have been over 100,000 confirmed cases of mpox (both clades), including over 200 deaths in confirmed cases. The DRC remains the country with the highest number of cases and deaths, followed by neighbouring Burundi.

Mpox - here's what you need to know

The symptoms of mpox may begin within a week of someone being exposed to the virus, but they can start up to three weeks after exposure. Symptoms typically last between two to four weeks, although they may last longer in someone with a weakened immune system. 

Common mpox symptoms are:

• a rash, which then blisters
• fever
• sore throat, cough, blocked nose
• headache
• muscle aches
• back pain
• low energy
• swollen lymph nodes (bean-shaped glands throughout the body)

The rash begins as a flat sore which develops into a round, pus-filled blister. This may be itchy or painful and is often discoloured in the centre.

As the rash heals, the lesions dry up, crust over and fall off. Some people have lots of sores, while others may only have a few. These can appear anywhere on the body and are often seen at the site of initial infection.

Mpox spreads through direct, interpersonal contact with someone who has the virus. Although this is mainly through touching infectious skin, and parts of the body where there are lesions, it can be passed on through respiratory droplets from prolonged close contact. 

Direct contact includes:

• skin to skin
• face to face
• mouth-to-mouth
• mouth-to-skin contact

Mpox can spread easily to other members of the household and sex partners. People with multiple sexual partners are at higher risk. It is also possible for people who are pregnant to pass mpox to their unborn child, and during and after, birth.

People are considered infectious, and can spread the disease, until their lesions have crusted over and the scabs have fallen off, with a new layer of skin formed underneath the pox. 

Animal-to-human transmission of mpox occurs from infected animals to humans from bites or scratches, or during activities such as hunting, cooking, and eating animals. It is unknown what the animal reservoir (where the virus naturally lives, grows, and multiplies) is for mpox, although mammals such as monkeys and squirrels can get infected.

People can also catch mpox from contaminated objects such as clothing or bedding. It can also be caught from a contaminated needle, for example through a needle-stick injury in a health care setting, or through tattooing. There is at least one example of mpox lesions appearing directly on a new tattoo.

The mpox virus is related to the smallpox virus, which was eradicated globally at the end of the 1970s because of the success of that vaccination programme. Because of the similarities between the two viruses, vaccines that were developed to prevent smallpox are being used against mpox.

Evidence from the 2022 – 2023 clade II outbreak suggests the vaccine is 70% to 85% effective, if given before exposure. Two doses are needed for best protection. The vaccine is expected to work as well for clade I.

While mass vaccination is not currently recommended by the WHO, the organisation advocates vaccination for people who are at risk. This includes, for example, if they have been in close contact with someone who has mpox, or belong to a group at high risk of exposure.

In the UK, the Modified Vaccinia Ankara – Bavarian Nordic (MVA-BN) vaccine is offered to people considered at high risk.  Two doses are needed for the best protection.

MVA-BN is sold under two trade names; Imvanex in the UK and Jynneos in the US. The MVA vaccine uses a much weakened form (attenuated) of a pox virus called vaccinia to induce an immune response. 

Globally, the WHO recommends two other vaccines – LC16 and ACAM2000.  These also use greatly weakened versions of the vaccinia virus. However, these aren’t recommended for some people, such as those who are immunocompromised or pregnant.

The mpox vaccine can be given either before exposure to the virus, or after an exposure. This may be offered up to 14 days after exposure to the virus to reduce the symptoms of the disease for those who do not already have symptoms.

This may be considered in those at higher risk of serious monkeypox infection (children under five years of age, the immunosuppressed and pregnant women).But the vaccine is less effective post-exposure and rarely given.

For more information about the mpox vaccine, please head to our mpox vaccine pages.

There is no specific treatment for mpox and patients are recommended supportive care, either at home if they are relatively well, or in hospital if they are very ill. It is important that someone with a confirmed case of mpox avoids spreading it to others whilst they are infectious.

Although mpox now mainly spreads from human to human, it originally spread from animal to human (zoonotic). It still spreads this way. Cases are often found close to tropical rainforests, as with the DRC, where there are animals that carry the virus. Mpox infection has been found in monkeys, as well as squirrels, Gambian pouched rats and dormice.

Mpox has been reported in the DRC for over a decade, with cases increasing each year. Last year, cases rose more sharply. Between January 2023 and the end of August 2024, the DRC reported more than 21,000 suspected cases, and 700 deaths. The majority of deaths (82%) have been reported in children under the age of 15.

Most of the DRC’s provinces have now reported cases of any strain. The new virus strain, clade Ib, which emerged last year is spreading rapidly. During August over 100 confirmed cases of clade Ib were also reported in four neighbouring countries—Burundi, Kenya, Rwanda, and Uganda—that had not previously reported mpox. Experts believe the actual number of cases is likely to be higher since many suspected cases have not been tested.

The virus is thought to be spreading through sexual networks, as well as close household contacts, and in healthcare settings that lack sufficient personal protective equipment for workers.

On 14 August 2024 the WHO declared the most recent outbreak a Public Health Emergency of International Concern (PHEIC). This means there is risk to public health internationally and a coordinated international response is required to try to prevent the further spread of the disease.

The WHO has started the process of speeding up the approval of mpox vaccines for use in emergencies.  This will make it easier for countries, which haven't approved the vaccines yet to get access to them. It also allows organisations like Gavi, the Vaccine Alliance and UNICEF to buy and distribute these vaccines more quickly.

Previously in May 2022, when cases broke out globally, the outbreak mainly affected men who are gay, bisexual, or have sex with other men. But it is important to note that anyone can catch and spread mpox. The risk of severe disease is higher in young children, pregnant women, people with eczema, and immunosuppressed individuals, such as people living with HIV. 

Mpox outbreak in the UK  

Between 2018 and 2022, the UK had only a few cases of mpox; all were Clade II and originated from West Africa. The spread was effectively contained through quick diagnosis, isolation, and care at designated centres. Close contacts were quarantined and monitored, and post-exposure vaccination was recommended to prevent serious symptoms.

However, in April/May 2022, three separate cases of mpox were identified. The first case involved an imported case from Nigeria but this didn't lead to further transmission. The second case suggested local transmission (caught within the UK), with an initial case having no travel history infecting two household members.

The third incident seemed to indicate transmission primarily among gay, bisexual, and other men who have sex with men. By September 2022, over 3,500 confirmed cases had been reported, predominantly in London, with the majority affecting males. The outbreak shows connections to similar cases globally, including in Canada, Portugal, Belgium, and Germany.

Between 2023 and July 2024 there were 286 mpox cases in the UK, some of which were acquired in the UK, some overseas. To date, there have been no Clade 1b cases reported in the UK, although Thailand and Sweden have reported one case each.