Mpox vaccine

Mpox is an infectious disease caused by the monkeypox virus. This can cause a painful skin rash, fever, headache, enlarged lymph nodes, as well as muscle aches, along with other symptoms. Most people fully recover. But some people may become very ill and the disease can be fatal.

Outbreaks have most commonly occurred in East, West or Central Africa. But mpox has been found in many other countries globally, including the UK. This is particularly the case since 2022.

There are currently two types (clades) of mpox circulating; clade 1 and clade 2. Clade 2 is behind the global outbreak that began in 2022. Although this outbreak has declined substantially since its peak, cases are still around.

And the World Health Organization (WHO) is concerned about the emergence of a new version of clade 1 (clade 1b) as it appears to cause more severe disease and a higher death rate than other clades.

So far, clade 1b mpox has been detected in the DRC and a few surrounding countries. Global cases have also been detected, with a handful of cases, who all share a household, being detected in London. 

In August 2024, the WHO declared the emergence of this new mpox clade a Public Health Emergency of International Concern (PHEIC) to enable an international response to prevent both this new mpox outbreak and existing outbreaks. Please go to our mpox infectious disease information for more detail.

Vaccines are available for people recommended vaccination (see section below). 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.

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, two other vaccines are recommended by the WHO – 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 has taken place. The vaccine is less effective post-exposure and rarely given.

Mpox - here's what you need to know

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

The UK pre-exposure vaccination programme

In the UK the MVA vaccine is being offered to people most likely to be exposed to mpox. This includes:

• healthcare workers looking after people who have confirmed, or suspected, mpox infection, including in High Consequence Infectious Disease (HCID) units
• men who are gay, bisexual or have sex with other men, and who have multiple partners, participate in group sex or attend or work at sex-on-premises venues 

For these last groups, the UK NHS mpox outbreak vaccination programme is currently only available in London and Greater Manchester, after the wider outbreak programme ended in July 2023.

Staff who work in specialist roles may also be offered the vaccine. These include:

• designated staff in sexual health clinics who assess mpox patients
• workers in laboratories where pox viruses are handled or cultured, or in highly specialist laboratories undertaking procedures with a significantly higher risk of exposure
• staff regularly undertaking environmental decontamination around cases of mpox

Two doses of the vaccine are recommended for the best protection, with the second dose given two to three months after the first.

People who may be sensitive to the ingredients or trace residues should not have this vaccine. See the full list in the ingredients section below.  As a precautionary measure, it is also best to avoid giving this vaccine during pregnancy or breastfeeding.

All vaccines have to undergo rigorous testing before they are approved for use. The MVA vaccine is no exception. The following side effects are described in the patient information leaflet for MVA-BN:

Very common (may affect more than 1 in 10 people):

• headache
• aching muscles
• feeling sick
• tiredness
• pain, redness, swelling, hardness or itching at the injection site

Common (may affect up to 1 in 10 people):

• chills
• fever
• joint or limb pain
• loss of appetite
• lump, discolouration, bruising or warmth at the injection site

Uncommon (may affect up to 1 in 100 people):

• nose and throat infection, upper respiratory tract infection
• swollen lymph nodes
• abnormal sleep
• dizziness, abnormal skin sensations
• muscle stiffness
• sore throat, runny nose or cough
• diarrhoea or vomiting
• rash, itch, or skin inflammation
• bleeding or irritation
• underarm swelling, feeling unwell, flushing, chest pain or pain in the armpit,
• change in blood test results (see patient information leaflet for more information)

Rare (may effect up to 1 in 1000 people):

• sinus infection
• influenza, or influenza-like illness
• redness and discomfort in the eye
• hives
• skin discolouration, bruising, or lump in skin
• sweating, or night sweats
• body/muscle/abdominal pain or cramps
• swelling of the ankles, feet or fingers
• faster heartbeat
• ear and throat ache
• dry mouth
• migraine, drowsiness, or spinning sensation (vertigo)
• nerve disorder causing weakness, tingling or numbness
• scaling, inflammation, abnormal skin sensation, reaction at the injection site, rash, numbness
• dryness, movement impairment, vesicles at the injection site
• swelling of the face, mouth and throat
• white blood cell count increased

As with any vaccine, medicine or food, there is a very small chance of a severe allergic reaction (anaphylaxis). Anaphylaxis is different from less severe allergic reactions because it causes life-threatening breathing and/or circulation problems. It is always extremely serious but can be treated with adrenaline. Healthcare workers who give vaccines know how to do this.

In the UK between 1997 and 2003 there were a total of 130 reports of anaphylaxis following ALL immunisations, although no deaths as a result of the reaction were reported. Around 117 million doses of vaccines were given in the UK during this period. This means that the overall rate of anaphylaxis is around 1 in 900,000.

If you are allergic to any of the vaccine constituents or if you are concerned about any reactions that occur after vaccination, consult your doctor. In the UK you can report suspected vaccine side effects to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card Scheme.

You can also contact the MHRA to ask for data on Yellow Card reports for individual vaccines. See more information on the Yellow Card scheme and monitoring of vaccine safety.

Apart from the active ingredients – Modified Vaccinia Ankara and Bavarian Nordic Live virus – the MVA-BN vaccine contains the following ingredients: 

• trometamol (used as a stabiliser)
• sodium chloride (salt)
• water

In addition, it may contain trace residues left over from the manufacturing process. This includes chicken protein and benzonase (used to purify virus particles), as well as several antibiotics, gentamicin and ciprofloxacin.

This vaccine is grown on chick embryo cells – see more information on our vaccine ingredients page.

People with known allergies to eggs, or the antibiotics mentioned above, should not be given this vaccine.  

 Please read the patient information leaflet for MVA-BN for more information.

JCVI Advice

The Joint Committee on Vaccination and Immunisation (JCVI), which makes recommendations to the UK Government on vaccine policy, released new advice in November 2023 about who should be vaccinated against mpox. 

The JCVI advises that pre-exposure vaccination (before the person comes into contact with the virus) should continue be offered to men who are gay, bisexual, or have sex with other men.

This group are at the highest risk of exposure to mpox, and are identified by sexual health services using similar criteria to that applied to HIV pre-exposure prophylaxis (PrEP) medication – medication that prevents HIV. This will be offered regardless of HIV status.

These risk criteria would include:

• a recent history of multiple partners
• participating in group sex
• attending sex-on-premises venues
• a proxy marker, such as a bacterial sexually transmitted infection (STI) within the last year

The JCVI also advise that efforts should be made to ensure that the vaccine is offered equitably to those at equivalent risk, including transgender women or gender-diverse people assigned male at birth.

Intradermal vaccination

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Most vaccines are given by injection into the muscle of the upper arm or thigh. This is called ‘intramuscular’ and many healthcare workers are trained to do this. But the product characteristics of the MVA vaccine recommend that it is given below the skin,  which is called ‘subcutaneous’.

Some vaccines can also be injected into the middle layer of the skin itself – this is known as intradermal vaccination. This requires specially trained staff and is done with a smaller volume (about one-fifth) of vaccine and uses a smaller needle and syringe.

Most vaccines require a smaller dose if given this way. This technique has been used commonly during outbreaks of other infections, such as yellow fever. When vaccines are injected into the skin, rather than the muscle, the important proteins in the vaccine are accessible to the cells of your immune system. This means that your body can make a good response to the vaccine. 

A study in 2015 compared different doses, formulations and methods of giving the MVA vaccine in 524 people. They received either 0.5mL subcutaneous dried or liquid vaccine or 0.1mL intradermally.

After the second dose, the overall response rates were around 95% in both groups receiving the liquid vaccine subcutaneously or intradermally. On the basis of this evidence, JCVI has said that intradermal vaccination is considered equivalent to the standard route. With supply constraints, the MVA vaccine is administered in the UK this way.

Intradermal monkeypox vaccination: What you need to know