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Mpox (previously called monkeypox) is a rare infectious disease caused by the mpox virus (MPXV). MPXV is a DNA virus related to but distinct from the viruses that cause smallpox and cowpox. Since smallpox was eliminated in 1980 and the smallpox vaccination programme ended, mpox has now become the dominant cause of orthopox outbreaks in humans.
There are two distinct viral clades:
| Viral clade | Description | Sub-clades |
|---|---|---|
| Clade I |
|
Clade Ia, Clade Ib |
| Clade II |
|
Clade IIa, Clade IIb |
Since May 2022, mpox cases have been reported in several countries, where the virus had not previously been found, including the UK. Most of these cases are from Clade IIb.
Historically, Clade I mpox has been known to circulate in a few Central African countries. However, in 2024, Clade I mpox cases were reported in countries outside this region, including the UK.
Mpox (any clade) is a notifiable disease.
Transmission
Human-to-human transmission occurs through close physical contact, including:
Direct contact with rash, skin lesions or scabs: The virus in skin lesions can infect others through breaks in the skin or mucosal membranes. Although mpox is not classified as a sexually transmitted infection, it can spread during sex, kissing, cuddling or other skin-to-skin contact.
Body fluids: Contact with bodily fluids such as saliva, snot or mucous, including during intimate sexual contact.
Respiratory droplets: The virus is also found in the upper respiratory tract and can spread through respiratory droplets during direct and prolonged face-to-face contact.
Contaminated material: Touching contaminated items like clothes or bedding that have been in contact with an infected person.
Mpox can also spread through close contact with an infected animal. Additionally, the virus may also be passed from mother to baby during pregnancy or birth.
Typically, mpox has an incubation period of between 5 and 21 days, but typically 6 to 13 days following exposure.
Clade II UK outbreak May 2022
In May 2022, the UK declared a national incident due to a rise in mpox cases, mainly among gay, bisexual, and other men who have sex with men (GBMSM). Following this, the UK introduced a targeted pre-exposure vaccination strategy to protect those most likely to be exposed to the virus. This included GBMSM identified by sexual health services and healthcare workers at high risk of exposure.
Due to vaccine supply, the initial focus was to deliver first doses to as many GBMSM at greatest risk of mpox as possible. By September 2022, with many doses delivered, declining mpox cases and sufficient vaccine supply, a second dose was recommended for high-risk individuals. The second dose was advised two to three months after the first dose to ensure longer protection.
Clade I mpox outbreak: 2024 to 2025
On 14 August 2024, the World Health Organisation (WHO) declared a Public Health Emergency of International Concern due to a rise in Clade I mpox cases in the Democratic Republic of the Congo and other African countries. This outbreak is still ongoing, with evidence of continued community transmission in a number of countries.
Clade I mpox cases linked to travel have been reported outside the African Region. Although there is currently no evidence of sustained community transmission of Clade I mpox outside of Africa, some local transmission (such as within households) has been reported in Belgium, China, France, Germany and the United Kingdom.
For the most up to date information, visit: Mpox: affected countries - GOV.UK (external site)
Routine pre-emptive vaccination strategy from 1 July 2025
In November 2023, the Joint Committee on Vaccination and Immunisation (JCVI) recommended a routine targeted vaccination strategy to protect those at greatest risk of mpox infection. In 2025, Welsh Government confirmed a routine vaccination programme to prevent mpox outbreaks. The vaccine is offered opportunistically as a pre-exposure vaccination through specialist sexual health services to GBMSM who are assessed as being at higher risk of mpox infection.
GBMSM attending sexual health services should be assessed by a sexual health clinician who will advise vaccination if they:
have a recent history of multiple partners,
participate in group sex,
attend ‘sex on premises’ venues, or
have had a bacterial sexually transmitted infection (STI) within the last year.
The vaccine may also be offered to those with similar risk levels. This includes people of any gender or sexual orientation. However, this will require a full clinical risk assessment to determine eligibility.
The vaccine available is the Modified Vaccinia Ankara (MVA-BN) vaccine.
The MVA-BN vaccine, originally designed for smallpox, offers a good level of protection against mpox. During the 2022 mpox outbreak, the vaccine’s effectiveness was estimated between 74-83%. The vaccine also helps reduce disease severity, with an estimated 67% effectiveness in preventing hospitalisation.
The MVA-BN vaccine has been authorised for active immunisation against mpox in adults by the UK by the Medicines and Healthcare Products Regulatory Agency (MHRA). There are two versions of this vaccine: Imvanex, made in Europe, and Jynneos, the US version. They are the same vaccine (manufactured by Bavarian Nordic) but come in different packaging.
The summary of product characteristics (SmPC) for Imvanex can be viewed on the MHRA website:
The package insert for Jynneos can be viewed on the US FDA website:
The vaccine can be administered by the subcutaneous or intramuscular route (see Immunisation procedures: Green Book chapter 4 (external site) ). The preferred site is the deltoid region of the upper arm.
The virus used in the vaccine is a replication-defective virus (also known as replication-incompetent virus). The virus used in the vaccine is also attenuated, so it cannot replicate in mammalian cells. It should be considered an inactivated vaccine.
The MVA-BN vaccine is a black triangle vaccine and therefore subject to additional monitoring. This will allow quick identification of new safety information. Healthcare professionals are asked to report any suspected adverse reactions using the Yellow Card reporting scheme (external site).
Most eligible people will require two doses. The second dose should be given at least 28 days after the first dose.
If the MVA-BN course is interrupted or delayed, it should be resumed using the same vaccine, but the first dose does not need to be repeated.
People who have previously been vaccinated against smallpox with the live smallpox vaccination will only require a single dose of the MVA-BN vaccine.
Refer to the Green Book Chapter 29 Smallpox and mpox - GOV UK (external site) and the Welsh Medicines Advice Service (external Site) for further information.
Most health and social care workers are at very low risk of mpox exposure and do not need a routine mpox pre-exposure vaccination. Staff working in specialist roles with frequent and prolonged exposure to orthopox viruses should be assessed by occupational health and offered vaccination if necessary. This includes:
Laboratory workers who handle or culture pox viruses (such as mpox or genetically modified vaccinia), including those in highly specialist laboratories.
Staff caring for in-patients with mpox in high consequence infectious disease (HCID) units, including those who clean areas where mpox patients have been cared for.
Staff who regularly perform environmental decontamination around cases of mpox.
UK healthcare and laboratory staff deployed to respond to an mpox outbreak or incident overseas.
UK humanitarian aid workers going to live and work in close contact with the local population in areas affected by an mpox outbreak or incident overseas.
Vaccination is not currently recommended for travellers. Current advice on avoiding mpox while travelling is available on the Travel Health Pro website: NaTHNaC - Mpox (external site)
The aims of post exposure immunisation are to prevent infection and reduce the severity of the disease in individuals who have been exposed to mpox.
Post exposure vaccination should be considered for those with the highest exposure risks (this is defined in the Contact tracing guidance for mpox - GOV.UK (external site))
There is growing evidence that post-exposure vaccination has low effectiveness in preventing mpox infection. However, if given promptly it may have the potential to prevent infection and/or to reduce the severity of the disease. Individuals should be risk assessed by a Health Protection team and the vaccine should be prioritised for those most likely to benefit from it. For example, individuals very recently exposed to mpox or those at higher risk of severe disease following infection.
Post-exposure vaccination of high-risk community or occupational contacts should ideally be offered within 4 days of exposure. However, it may be offered within 14 days in those at ongoing risk, or for those who are at higher risk of complications from mpox. For example:
children (below the age of five years),
pregnant women, and
individuals with severe immunosuppression.
Any exposure event may provide a chance to offer a first or second dose of the vaccine to individuals who have not yet been vaccinated. This applies to those eligible for pre-exposure vaccination, such as GBMSM at risk of mpox and certain health care workers.
Refer to Smallpox and mpox: Green Book, Chapter 29 and Contact tracing guidance for mpox - GOV.UK (external site) for further information.
The MVA-BN vaccine is a non-live vaccine, so it can be given with live vaccines and in people taking PrEP. It can also be given at the same time as the MenB, HPV, hepatitis A and hepatitis B vaccines.
Vaccination programme recommendations from the Joint Committee on Vaccination and Immunisation (JCVI) and Welsh Government policy can be found at the links below.
Joint Committee on Vaccination and Immunisation - GOV.UK (external site) (read JCVI publications and statements; search e.g. Mpox)
Public Health Alerts / Contacts: Policy, letters and Welsh Government (sharepoint.com)
Welsh Health Circulars and Welsh Government letters: Mpox (Monkeypox) vaccination programme | GOV.WALES (external site)
Online courses and training materials about a number of vaccines and diseases can be accessed via the E-learning page.
Further immunisation training information and resources are provided on the Training Resources and Events page.
Vaccination toolkit for sexual health services healthcare practitioners
Vaccine PGD templates and Advisory Documents for Wales can be found on the Welsh Medicines Advice Service (external site) web page.