Guidance

Mpox vaccination: information for healthcare practitioners

Published 7 April 2025

Applies to England

This information guidance is about the routine mpox vaccination programme for high-risk gay, bisexual and other men who have sex with men (GBMSM). It does not cover vaccination response in the event of an outbreak or incident, or vaccination based on occupational health risk assessments as separate resources are available in the smallpox and mpox green book chapter and mpox: guidance collection. Please ensure the correct guidance for the programme you are delivering is used.

Background

Mpox is a disease caused by infection with the virus MPXV. MPXV is related to, but distinct from, the viruses that cause smallpox (variola virus) and cowpox (vaccinia virus). There are 2 genetic groups of MPXV: clade I and clade II.

Before spring 2022, UK mpox cases were either associated with travel to or from countries where mpox is endemic (mostly countries in West or Central Africa) or had documented epidemiological links to these cases.

In May 2022, sustained transmission of MPXV (clade II) was identified in the UK leading to a large outbreak different to the pattern and scale that had previously been observed. Cases were primarily identified among gay, bisexual and other men who have sex with men (GBMSM) without a history of travel to endemic countries. Epidemiological surveillance suggested that transmission was occurring from direct person-to-person contact in defined sexual networks of GBMSM.

At that time there was no vaccine licensed for protection against mpox. However, there was good evidence that the Modified Vaccinia Ankara - Bavarian Nordic (MVA-BN) smallpox vaccine would provide cross-protection to mpox when given pre-exposure. In September 2022, the Medicines and Healthcare products Regulatory Agency (MHRA) approved MVA-BN for vaccination against mpox.

As an outbreak response, a limited offer of pre-exposure vaccination was recommended in GBMSM who may be at highest risk of exposure to mpox and as occupational vaccination to workers at high risk of exposure.

In June and September 2023, the Joint Committee on Vaccination and Immunisation (JCVI) met to discuss the potential for a routine mpox immunisation programme. A model of the impact and cost-effectiveness of reactive (initiating a programme in response to an outbreak) and pre-emptive scenarios (offering vaccination as a routine programme) was reviewed. In November 2023, JCVI recommended that a routine vaccination programme for protection of GBMSM at highest risk of exposure to mpox, offered through sexual health services, should be developed to prevent future outbreaks (JVCI statement on mpox vaccination as a routine programme).

The JCVI advised that pre-exposure vaccination should target GBMSM who are at highest risk of exposure to mpox, identified via sexual health services using markers of risk to assess eligibility. These risk criteria include a recent history of multiple partners, participating in group sex, attending sex-on-premises venues or based on proxy markers such as recent bacterial sexually transmitted infection (in the past year). Other individuals who have frequent close and intimate contact with the GBMSM network at risk of mpox may also be vaccinated, irrespective of their identified gender. This would include staff who work in GBMSM sex-on-premises venues, such as saunas, if they are regularly exposed to items (for example, linen) or surfaces likely to be contaminated with body fluids or skin cells.

About mpox

Human mpox was first described in 1970 when regional elimination of smallpox revealed sporadic cases of a disease with similar presentation in rural areas of the Democratic Republic of Congo. Outbreaks have since occurred in Nigeria, Republic of Congo, Sierra Leone, Liberia, Cameroon and the Central African Republic.

MPXV spread may occur when a person comes into close contact with lesions, body fluids (including during intimate sexual contact), or respiratory droplets from an animal or human with the infection; or from contact with material contaminated with the virus, such as bedding. The virus enters the body through broken skin, the respiratory tract or the mucous membranes. The time from MPXV exposure to disease onset (incubation period) can be 5 to 21 days, but on average takes 6 to 13 days. Most patients experience a mild, self-limiting illness, with spontaneous and complete recovery seen within 3 weeks of onset. However, severe illness can occur and sometimes results in death. The risk of severe disease is higher in children, pregnant women and severely immunosuppressed individuals.

There are 2 genetic groups of MPXV: clade I (previously known as Central African or Congo Basin clade) and clade II (previously known as the West African clade).

MPXV disease was classified as a high consequence infectious disease (HCID) in 2018 meaning that all cases were managed via HCID pathways in healthcare settings. Evidence supporting low case fatality rate, and a mild to moderate severity illness accumulated for clade IIb, and in January 2023, and the Advisory Committee on Dangerous Pathogens (ACDP) advised that clade II mpox no longer met the criteria for a HCID. In March 2025, it was announced that the ACDP had recently assessed evidence gathered by UKHSA for clade I mpox and advised that it also no longer met the criteria of a HCID. It remains a serious infection for some individuals.

Aim of the routine mpox vaccination programme

Mpox vaccination provides protection against infection and severe disease. The aim of the routine mpox vaccination programme is to prevent future outbreaks and protect those at risk of exposure. An established routine programme allows vaccines to be consistently offered pre-exposure, through sexual health services on an ongoing basis.

Eligibility

As vaccine supply becomes available, the routine mpox vaccination programme in sexual health services across the UK is being stood up.

The MVA-BN vaccine should be offered to individuals who identify as GBMSM and are assessed as being at risk of mpox exposure as outlined in Smallpox and mpox: the green book, chapter 29, namely:

• a recent history of multiple sexual partners
• participation in group sex
• attendance at sex-on-premises venues
• acquired a bacterial sexually transmitted infection (STI) in the last 12 months

Vaccination should also be offered to individuals (irrespective of gender or sexual orientation) who have frequent close and intimate contact with the GBMSM network at risk of mpox, such as staff working in sex-on-premises venues frequented by GBMSM individuals and who are regularly exposed to surfaces or linen likely to be contaminated with body fluids or skin cells (such as in saunas).

MVA-BN Vaccine

Live modified vaccinia Ankara (MVA) vaccine, manufactured by Bavarian Nordic (BN) is known as Imvanex® in the UK and Europe and has been used since 2013 for the prevention of smallpox. Since September 2022, MVA-BN vaccine has also been approved for immunisation against mpox (regardless of MPXV clade) in the UK by the Medicines and Healthcare products Regulatory Agency (MHRA). The same MVA-BN vaccine is licensed by the Food and Drug Administration (FDA) and known as Jynneos® in the US.

The MVA-BN vaccine is the only vaccine currently available for use within the UK routine mpox immunisation programme.

Studies in adults and children show that protection including the production of antibodies against MPXV occurs following MVA-BN vaccination. Estimates of real-world vaccine effectiveness (VE) in preventing mpox infection have been mainly generated during the 2022 outbreak. In these studies, VE was estimated to be around 76% and 82% respectively for one and two doses of MVA-BN vaccine. There was also evidence that pre-exposure vaccination may modify disease, reduce severe presentations, the number of body regions affected by a rash and/or reduce the rate of hospitalisation​.

Observed data in 2023 suggests that protection following MVA-BN vaccination is approximately 5 years for one dose and 10 years for two doses. There is limited data to determine the need and appropriate timing of booster doses so these are only currently recommended in certain circumstances (see Green Book Mpox chapter)

How the vaccine works

The modified vaccinia Ankara (MVA-BN) vaccine contains a replication-defective (also known as replication-incompetent) virus. Vaccinia (the virus used to make the vaccine), is an orthopoxvirus, similar to smallpox and MPXV, but less harmful. The virus used in the vaccine is attenuated (weakened) through multiple passages (repeated growth cycles of the cells on a culture) in chicken embryo fibroblast cells. This leads to a substantial loss of its genome (genetic information) and many of the known immune evasion (ability to avoid detection by the immune system) and virulence (ability of the virus to cause damage in the body) factors are not encoded. This means that the immune system can detect the mpox virus in the vaccine and enable the body to generate protection safely.

In human and animal studies, the virus used in the vaccine does not replicate very well but still stimulates the body to produce protective immune responses against mpox, smallpox and other orthopoxviruses. Because the virus used in the vaccine has been attenuated to ensure it cannot replicate in mammalian cells, this also means that it does not produce a lesion at the site of vaccination​ in the way that the older smallpox vaccines used to.

Even though the vaccine virus is live, it has been modified so that it does not replicate in humans which means it should be considered as an inactivated vaccine and can be safely given to individuals who are immunosuppressed. The vaccine does not contain the smallpox or mpox virus and cannot cause either disease.

How intradermal vaccination works

While the MVA-BN vaccine is usually administered via the intramuscular (IM) or sub-cutaneous (SC) route, the intradermal (ID) route is also used. ID immunisation can be very effective, often requiring a fractional (smaller) dose of vaccine compared to the SC or IM routes. This is because the dermis (the middle layer of skin into which the vaccine is administered) contains lots of antigen-presenting cells. These antigen-presenting cells ‘capture’ the antigens from the vaccine and migrate to the lymphatic system where further immune responses generate protection. Because of the large volume of antigen-presenting cells in the dermal layer of the skin, a much smaller dose compared to the standard SC or IM dose of vaccine is usually required to stimulate an immune response when administered via this route. Intradermal injection technique requires additional training before being performed.

When given via the ID route, up to five 0.1ml doses may be obtained from a single MVA-BN vial. If the amount of vaccine remaining in the vial cannot provide a full dose of 0.1 ml, the vial and its remaining contents must be discarded. Excess vaccine must not be pooled from multiple vials because such practice will increase the risk of potential contaminants or that an insufficient dose is given.

Using Jynneos® in the UK

Medicines can only be routinely used in the UK if they are licensed by the MHRA or the European Medicines Agency (EMA).

Although Imvanex® (the UK-labelled version of the MVA-BN vaccine) has been licensed by the EMA and authorised for use in the UK by the MHRA, some of the US-licensed vaccine Jynneos® was urgently procured to ensure the UK had enough vaccine to manage the mpox outbreak in 2022. Jynneos® is licensed for use by the US FDA but not the MHRA or EMA so batch specific variation by the MHRA was required before importation and use of the vaccine was allowed in the UK. A batch specific variation is an agreement to allow an identified batch (or small number of batches) of a product (with the same quality, safety and efficacy as the original product) to be released for use outside of the usual process when an unexpected or unavoidable situation has occurred. A specific batch of the Jynneos® vaccine was imported which has the batch number FDP00072.

Depending on what is available from centrally held stocks at the time of ordering, either Jynneos® or Imvanex® will be supplied.

While all batches of Imvanex® can be used under the PGD, where Jynneos® is the local vaccine available at time of administration, the mpox PGD valid from 10 October 2024 only enables the use of Jynneos® vaccine: batch number FDP00072 (expiry date 31 July 2025). If further Jynneos® is procured and supplied in the future, vaccinators must check that batch can be administered via the current PGD. An alternative framework (such as a PSD) will be required if the current PGD does not enable the use of the Jynneos® batch supplied.

MVA-BN vaccination of individuals under 18 years of age

It is possible that individuals under the age of 18 years may attend sexual health clinics and be assessed as at risk of mpox exposure as outlined in Smallpox and mpox: the green book, chapter 29.

Imvanex® is licensed for use in adults aged 18 years and older by the MHRA. Jynneos® is licensed by the FDA for use in people aged 18 years and over. Mpox is known to be more serious in young children so the JCVI recommend the use the MVA-BN vaccine (either Imvanex® or Jynneos®) in all individuals who are eligible, regardless of age. The vaccines have been given safely to a number of children in the UK and appear to work very well. They have an acceptable safety record, causing very similar side effects to other vaccines. This means MVA-BN vaccine should be given off-label to adolescents, children and babies when indicated.

MVA-BN vaccine and co-administration with or intervals between other vaccines

Although no data on co-administration of MVA-BN vaccine with others exists, first principles of immunisation suggest that interference between inactivated vaccines with different antigenic content is likely to be limited which means that MVA-BN vaccine can be given at the same time as other vaccines. Based on experience with others, administering the MVA-BN vaccine alongside other vaccines is most likely to result in a slightly weakened response to one of the vaccines but there is no evidence of any safety concerns. As the MVA-BN vaccine is considered inactivated, it can still be given if individuals have recently received one or more inactivated vaccines, regardless of the interval. MVA-BN can also be co-administered with live vaccines and in those on HIV PrEP.

When an individual is eligible for vaccination against different diseases, where possible all vaccines should be given at the same visit to maximise benefit and reduce the time the person remains unprotected and at risk. There is no interval required for subsequent vaccines after IM or SC MVA-BN vaccination.

As mpox is a relatively new vaccine and may be given ID over the insertion of the deltoid aspect or forearm, it is preferable to only give that vaccine in the limb to avoid misattributing or confusing local reactions to other vaccines.

MVA-BN vaccine and the interval between doses

Information on doses and the recommended schedule for use of MVA-BN can be found in the green book chapter 29. Where a 2-dose course is required, there should be at least a 28-day interval between doses. 

Twenty-eight days is the minimum interval required between doses to generate a sufficient immune response. If the MVA-BN course is interrupted or delayed, it should be resumed but there is no need to recommence the primary immunisation schedule even after a prolonged interval between the 2 doses.

Potential issues or errors

Vaccination in the same limb following ID vaccination

Unlike BCG, there is no requirement to wait for 3 months before subsequent vaccination in the same limb following ID vaccination of MVA-BN. BCG is a live vaccine and no further immunisation should be given in the arm used for BCG immunisation for at least 3 months because of the risk of regional lymphadenitis

MVA-BN is a non-replicating vaccine so unlike BCG, does not replicate at the vaccination site before being transported to the lymph nodes. While it is preferable to avoid further vaccination in the limb used for ID MVA-BN if multiple vaccines are given on the same day, this is to avoid misattributing or confusing local reactions to other vaccines. Subsequent vaccinations (including BCG) can be administered in the arm used for MVA-BN vaccination once any localised reactions have resolved.

Vaccine administered via the incorrect route

A 0.5ml dose of vaccine is required when administered via the SC or IM route, but a 0.1ml dose is required for ID administration.

If the intended route of administration was SC but the 0.5ml dose was given via the IM route, or vice versa, then the dose does not need to be repeated.

If the ID dose of 0.1ml has inadvertently been given via the IM or SC route, then it cannot be assumed that the individual has received sufficient antigen to generate an immune response so the dose should be discounted and a full dose should be repeated immediately (or as soon as the error is realised) giving the correct amount for the route of administration. The repeated dose should be administered at least 5 cm from the original site where possible, and the recipient should be advised that they may be more likely to experience local and systemic adverse reactions. Use of a different limb is preferable but if this is not possible and ensuring a distance of 5cm is difficult (for example, in those with smaller anatomical sites such as children), the repeat dose can still be given, as long as it is given at least 2.5 cm from the previous dose.

If more than 0.1ml was given via the ID route, the dose does not need to be repeated, but the recipient should be advised that they may be more likely to experience local and systemic adverse reactions.

Incorrect and/or partial dose of vaccine administered in error

As discussed in the section above, a 0.5ml dose of vaccine is required when administered via the SC or IM route, but a 0.1ml dose is required for ID administration.

If 0.1ml of vaccine has inadvertently been given IM or SC, the dose should be repeated immediately (or as soon as the error is realised), giving the correct amount for the method of administration (0.5ml if given SC or IM, 0.1ml if given ID).

If less than the correct dose is given, for example because the recipient pulled away or some vaccine leaked out of the syringe as it was being administered, this should be discounted and the full dose should be repeated immediately, administered at least 5 cm, where possible, from the original site. Use of a different limb is preferable but if this is not possible and ensuring a distance of 5cm is difficult (for example, in those with smaller anatomical sites such as children), the repeat dose can still be given, as long as it is given at least 2.5 cm from the previous dose.

If more than 0.1ml has been given ID, the dose is valid and does not need to be repeated, but the recipient should be advised that they may be more likely to experience local and systemic adverse reactions.

Additional dose given in error

Common adverse events following vaccination include local site reactions and influenza-like symptoms which are self-limiting and mainly mild to moderate in intensity. ID injection appears to be associated with a higher rate of itchiness and local reactions such as redness and induration when compared to SC or IM injection although pain at the injection site seems to be less common. Studies show that adverse event rates reported after any vaccination dose (first, second or booster) are similar, but anecdotally the frequency of adverse events, particularly local site reactions, appears to be higher in those who had received previous live smallpox vaccine.

In the event of an additional dose being inadvertently administered, the individual should be advised that adverse reactions are likely to be consistent with those of a single dose. Symptomatic treatment such as paracetamol can be taken if required.

Vaccine given intradermally but no bleb is observed

A correctly given intradermal injection of 0.1ml, results in a tense, blanched, raised bleb of around 7mm diameter. If little resistance is felt when injecting and a diffuse swelling occurs as opposed to a tense blanched bleb, the needle has been inserted too deeply. In these instances, the needle should be withdrawn and a full dose repeated via the ID route immediately, where possible at a site at least 5 cm away. If it is not possible to give the repeated dose via the ID route, then the full dose can be given via the IM or SC route (0.5ml) if needed.  Use of a different limb is preferable but if this is not possible and ensuring a distance of 5cm is difficult (fore example, in those with smaller anatomical sites such as children), the repeat dose can still be given, as long as it is given at least 2.5 cm from the previous dose.

Subsequent dose of vaccine given too early

For pre-exposure vaccination of individuals not previously vaccinated against smallpox, a course of 2 doses with a minimum 28-day interval is required (see the green book chapter 29 or the mpox PGD for more information). Vaccines administered sooner than the recommended interval from the last dose may lead to a reduced immune response. Where the second dose of MVA-BN is given earlier than a 28-day interval, an individual risk assessment considering the risks and benefits of repeating a dose is required. This risk assessment should include how early the vaccine was administered and the risk to the patient of current/imminent exposure. This guidance may be updated as further evidence becomes available.

Inadvertent ID administration to someone with history of keloid scarring or immunosuppression

Keloid scarring is an excessive growth of scar tissue due to an overproduction of collagen which results in a raised, thick, irregular growth that may become larger than the original wound. Individuals with a history of keloid scarring should not be vaccinated via the intradermal route as scarring following intradermal administration is noted to be higher in this group. Treatment is difficult, but if inadvertently vaccinated via this route, individuals should be advised of the error and referred to their GP or specialist for review as topical corticosteroids or alternative treatment which could reduce risk of scarring may be required.

As individuals who are immunosuppressed (as defined in chapter 28A of the green book) may mount less of an immune response to vaccines compared to individuals who are immunocompetent, the ID route of administration of the mpox vaccine is not routinely recommended. The SC or IM routes should be used instead. ID vaccination in this cohort is acceptable for localised outbreak use during periods of supply constraints when there is no alternative, but in the event of it being given in error, a risk assessment should be undertaken to consider the extent of immunosuppression and need for revaccination with a 0.5ml dose via the SC or IM route because of the possibility of increased reactogenicity following receipt of an additional dose.

Further resources

Healthcare practitioner resources to support the routine mpox programme including the Green Book smallpox and mpox chapter, a training slide set, and a video of the intradermal technique for administering the MVA-BN vaccine are available on the Mpox guidance collection site. The UKHSA mpox vaccine PGD is also available on the UKHSA PGD templates collection page ready for local authorisation.

To order social media graphics, posters or patient leaflets to be delivered to you, please visit Health Publications and register for a health professional account. Searching for mpox should identify patient resources available.

For additional guidance about mpox, including guidance for healthcare professionals on diagnosis and management of mpox cases (all clades), guidance for non-healthcare settings, separate guidance for clade I and clade II mpox, consent forms and guidance for the public, see the UKHSA mpox: guidance collection.

The MVA-BN vaccine product information (SPC and PIL) is available on the MHRA website by searching for Imvanex.

Document History

Version Number	Change Details	Date
01.00	New information document created	October 2024