Mpox (previously known as monkeypox)

What

Mpox, previously known as monkeypox, is a viral zoonotic disease. Mpox is usually self-limiting, but it can cause severe illness, particularly in people who are immunocompromised, children, and pregnant women.

Who

Primary preventive vaccination (PPV) against mpox is recommended for groups at risk of exposure. This includes:

• gay, bisexual or other men who have sex with men (GBMSM), including transgender and gender-diverse people
• sex workers, particularly those whose clients are at risk of mpox exposure
• people with HIV, if at risk of mpox exposure 
• other individuals whose sexual networks might include GBMSM
• laboratory personnel working with orthopoxviruses

PPV may also be considered for:

• healthcare workers at risk of exposure to patients with mpox

Post-exposure preventive vaccination (PEPV) is recommended for anyone categorised by public health authorities as a high-risk mpox contact within the past 14 days. Risk assessment for people exposed to mpox (contacts) who are being assessed for PEPV is stratified by high, medium or low risk.

How

Mpox vaccination is recommended for both PPV and PEPV against mpox. JYNNEOS (a brand name of replication-deficient modified vaccinia Ankara– Bavarian Nordic, or MVA-BN) is the preferred vaccine for both PPV and PEPV, due to its favourable safety profile and comparative ease of administration. The recommended schedule is 2 doses, with a minimum interval of 4 weeks between doses.

Why

Mpox in humans is generally a self-limiting illness, but lesions may be painful and supportive treatment may be required, including hospital admission. Lesions may also leave pitted scars or discolouration.^1,2 The risk of severe disease is higher in children, pregnant women and people who are immunocompromised.

Mpox vaccines available in Australia

The non-replicating MVA-BN vaccine is available and in use in Australia. Available brands may vary depending on supply. MVA-BN vaccines available globally include JYNNEOS, Imvanex and Imvamune. The US Food and Drug Administration and European Medicines Agency websites provide relevant product information for MVA-BN. 

The MVA-BN vaccine is not registered for use in Australia and has been made available under s18A (emergency use provision) of the Therapeutic Goods Act 1989. It is approved for use in adults aged ≥18 years by the US Food and Drug Administration, United Kingdom Medicines and Healthcare products Regulatory Agency and other regulatory bodies. In Australia, people of any age who are in a risk group, can receive MVA-BN as primary preventative vaccination.

The replication-competent smallpox vaccine ACAM2000 is available in Australia and has been used infrequently against mpox. It involves more complex administration and has a less favourable safety profile than JYNNEOS. ACAM2000™ (Emergent BioSolutions) is available from the National Medical Stockpile on a request basis for State and Territory programs. 

See also Vaccine information and Variations from product information for more details.

Supply considerations may affect the availability of MVA-BN vaccines. Fractional intradermal dosing may be used as an alternative route of administration for primary preventive vaccination (PPV) only, as a dose-sparing strategy. 

Dose and route

A standard primary vaccination course of MVA-BN mpox vaccine requires 2 subcutaneous doses, each of 0.5 mL, given 4 weeks apart. Subcutaneous injection is the preferred route of administration. 

An alternative route of administration for MVA-BN is by intradermal injection. Each intradermal dose is 0.1 mL (20% of the standard subcutaneous dose). Intradermal injection is not the preferred route for the 1st dose of post-exposure preventive vaccination (PEPV). The intradermal route should only be used by suitably qualified and experienced providers. If giving MVA-BN mpox vaccine by the intradermal route, the 0.5 mL vial can be used for more than 1 person during a single vaccination session. Any remaining vaccine must be discarded at the end of the session. See Administration of vaccines. Providers should check the guidance from their state or territory prior to considering intradermal administration.

The subcutaneous and intradermal routes of administration for MVA-BN are considered interchangeable for the purpose of completing a 2-dose course for primary preventive vaccination (PPV). If the 1st dose of MVA-BN is administered subcutaneously for PPV, the second dose can be administered via the intradermal route, and vice versa. If a single subcutaneous dose of MVA-BN is given as PEPV, a 2nd dose can later be given either subcutaneously or intradermally, as completion of a primary course (see Recommendations).

Co-administration with other vaccines

Co-administration with an mRNA COVID-19 vaccine

Replicating mpox vaccines (such as ACAM2000) and mRNA COVID-19 vaccines both carry a slightly increased risk of myocarditis, but the risk from non-replicating MVA-BN mpox vaccines remains unknown. The United States Food and Drug Administration (FDA) has added “myocarditis, pericarditis” as an observed adverse reaction in the “Post-marketing Experience” section of the JYNNEOS product information.⁴ However, a causal relationship to vaccine exposure has not been established. 

If the timing of mpox vaccination is not urgent, consider administering MVA-BN and mRNA COVID-19 vaccines 4 weeks apart to minimise incorrect attribution of any adverse events. This is particularly relevant for people who are in a higher risk group for myocarditis, such as young males. However, this is precautionary only. Recent recipients of an mRNA vaccine should not delay administration of PEPV or PPV if protection is urgent.

Co-administration with other vaccine, including live vaccines

There are no data on co-administration of MVA-BN mpox vaccine, but inactivated (or non-replicating) vaccines can generally be co-administered safely with other vaccines. There may be a theoretical risk of an attenuated immune response due to vaccine interference with other live vaccines. However, if a person has recently received another live vaccine and they are recommended to receive mpox vaccine, they should receive MVA-BN for disease prevention. Similarly, if a person has recently received mpox vaccine, they can receive another live vaccine if recommended.

Contraindications

The only absolute contraindications to MVA-BN mpox vaccine are:

• anaphylaxis after a previous dose of any MVA-BN mpox vaccine
• anaphylaxis after any component or trace residue of an MVA-BN mpox vaccine

Contact your state or territory health authority for more details.

Precautions

People who are immunocompromised, including people with HIV

Although evidence is limited, the immune response to MVA-BN mpox vaccine is likely to be reduced in people who are immunocompromised, especially people who are severely immunocompromised. Specialist medical advice may be required, including consideration of additional doses for those at ongoing risk of exposure. 

Data from a key United States study showed adjusted vaccine effectiveness for two doses among immunocompromised participants was 70.2%, compared with 87.8% in immunocompetent participants.⁶ No safety concerns have been reported in immunocompromised populations to date, including hematopoietic stem cell transplant recipients.⁷

Clinical data on MVA-BN use in people with HIV infection are limited, but the vaccine appears to be well tolerated in these populations with no adverse impact on viral load or CD4 cell count.^8,9 One study reported similar antibody responses after the 2nd dose between participants with HIV (CD4 count ≥350 cells/mm³; seroconversion rate of 89%) and those without HIV participants seroconversion rate of 96%.10 Another study found significantly lower seropositivity rates in participants with HIV (CD4 count of 200–750 cells/mm³; seropositivity rate of 61%) compared with controls (seropositivity rate of 81%) after dose 2.9 In this study, when response in participants with HIV was stratified by CD4 count, there was a trend of lower geometric mean titre with decreasing CD4 count, though the differences were not statistically significant. A more recent study showed that the standard regimen of MVA-BN induced an adequate immune response in people with HIV, including those with a CD4 count <200 cells/mm3 at baseline.¹¹

People with atopic dermatitis or a history of keloid scarring

Local adverse reactions after subcutaneous MVA-BN are more common in people with atopic dermatitis, although the overall safety profile is similar.^12,13 Australian safety data show a higher rate of adverse events in people with atopic dermatitis when MVA-BN was administered either intradermally (dose 1: 81%; dose 2: 55%,) or subcutaneously (dose 1: 62%; dose 2: 47%), compared to the average adverse event rates for intradermal (dose 1: 53%; dose 2: 35%) or subcutaneous routes (dose 1: 47%; dose 2: 31%).²¹ People with atopic dermatitis should be informed about the potential for increased local and general symptoms. 

People with a history of keloid scarring are not recommended to receive MVA-BN mpox vaccine via the intradermal route. The subcutaneous route is preferred.

Woman who are pregnant or breastfeeding

MVA-BN mpox vaccine has not been formally evaluated in pregnant or lactating women, but limited animal studies have identified no vaccine-related fetal malformations.⁴ No adverse events have been reported from use of MVA-BN in pregnant women, though data are limited to fewer than 300 pregnancies.⁴

It is not known whether MVA-BN is excreted in human milk, but this is unlikely as the vaccine virus does not replicate effectively in humans. There are not likely to be any safety concerns with administering MVA-BN mpox vaccine to breastfeeding women.

People who are allergic to chicken or egg protein

MVA-BN mpox vaccine is cultured in, and harvested from chicken embryo fibroblast cells. These may contain trace residues of chicken or egg protein.¹⁴ People with a known severe allergy to chicken or egg protein who are recommended to receive mpox vaccine should discuss this with an immunologist or allergist, or be referred to a specialised immunisation adverse events clinic.

Adverse events after MVA-BN mpox vaccine via subcutaneous route

Safety data from both clinical trials and post-licensure observational studies for MVA-BN used in healthy adults were largely consistent. In randomised clinical trials, 74.6% to 98.1% of participants experienced any local adverse event and 35.9% to 80.5% experienced any systemic adverse event after vaccination.^{8-10,13,15-20} Post-licensure surveillance safety data from Australia and the United States showed a self-reported adverse event rate of 25% to 47%.^21,22 The most commonly reported local adverse events were injection site pain, redness, swelling and induration. The most commonly reported systemic adverse events were muscle pain, headache, fatigue, nausea and chills. 

Adverse event rates reported after any vaccination dose (1st, 2nd or booster) were similar. However, anecdotally the frequency of adverse events, particularly local site reactions, appears to be higher in people who had received a previous live smallpox vaccine.⁴ 

Serious vaccine-related adverse events have been very rarely reported in clinical trials. More than 1 million doses of MVA-BN were administered during the 2022 international mpox outbreak, with no major safety concerns identified. However, most doses were given to younger adult males (more than 90% of vaccine recipients were aged 18-49 years),²³ so safety data must be interpreted with caution. 

The United States Food and Drug Administration (FDA) has added “myocarditis, pericarditis” as an observed adverse reaction in the “Post-marketing Experience” section of the JYNNEOS product information.⁴ However, a causal relationship to vaccine exposure has not been established. 

Adverse events after MVA-BN mpox vaccine via intradermal route

Data from a clinical trial showed no significant differences in the frequency of systemic adverse events in healthy adults who received MVA-BN intradermally or subcutaneously.¹⁵ However, local reactogenicity (erythema and induration) was higher in the intradermal group (100%) than in the subcutaneous group (84.4%). A higher rate of moderate or severe local reactions was reported in the intradermal group (94.8%) than in the subcutaneous group (58.1%) and the reactions lasted longer in the intradermal group.  Mild injection site skin discolouration, nodules or other local reactions lasting longer than 30 days were reported in 25% (subcutaneous) up to 67% (intradermal) of participants, but this finding was not identified in other comparison studies of MVA vaccines.

Vaccine safety surveillance data from Australia and the United States reported a slightly higher rate of adverse events in people receiving MVA-BN via the intradermal route (dose 1: 53%; dose 2: 35%) compared to the subcutaneous route (dose 1: 47%; dose 2: 31%), but all the events were mild and local to the injection site.^22,24
 

Mpox disease is caused by the monkeypox virus. This is a DNA virus in the same family of viruses that causes smallpox (variola) and vaccinia (used in smallpox and mpox vaccines).

Pathogenesis

Mpox is an acute viral illness that is caused by exposure to an infected animal or person. The incubation period is 2–21 days, with an average of around 7-9 days in the recent global outbreak.²⁵

Transmission

Monkeypox virus can be transmitted from animals to people, or from person to person. The natural animal reservoir for monkeypox virus has not yet been identified, but the virus has been detected in primates, prairie dogs, squirrels and other rodents.^26-28 The recent global outbreak has been driven by human-to-human transmission.

People with mpox are infectious from the time that they develop their first symptoms (which may be a fever or a rash) until all skin lesions crust, scab and fall off with a layer of new skin forming underneath. The infectious period can last up to 4 weeks.²⁹

Transmission between people occurs primarily through close contact with rash, scabs or body fluids (including from sexual contact or kissing).³⁰ Transmission through respiratory droplets or contaminated objects may be possible, but current evidence suggests this is less likely to occur.^30,31 Vertical (mother to fetus) and peripartum transmission have also occurred.^31,32

Symptoms of mpox

Mpox typically includes a prodromal illness, followed by a rash within 2–4 days.33  Other common symptoms include:³³  

• fever
• swollen lymph nodes
• fatigue
• headache
• muscle aches

The rash begins as a flat sore and turns into blisters before scabbing over. It may occur anywhere on the body, including the face, hands, feet, groin and genital areas, or around the anus.³³

Symptoms typically last 2-4 weeks but may last longer in people who are immunocompromised.³⁴

Complications of mpox 

Complications of mpox include:

• secondary bacterial infection
• sepsis
• pneumonia
• encephalitis
• symptoms such as severe oropharyngeal or anorectal pain may lead to hospitalisation.²⁵ The risk of severe disease and complications is likely to be higher in people who are immunocompromised,³⁵ young children³⁶ and pregnant women.

There are two types of the virus that causes mpox: clade I and clade II. Clade I caused higher numbers of severe illnesses than clade II, with up to 10% of case fatality rates historically. The 2023 clade I outbreaks in Central and Eastern Africa have seen much lower death rates of about 1-3%.

The virus strain that caused the 2022 multi-country outbreak outside Africa is clade II (b lineage),³⁷ which has an overall case fatality rate of 0.1%.³⁸

Mpox global epidemiology

Mpox is a zoonotic viral illness that is endemic to rainforest areas of Central and West Africa. Human cases were first reported in 1970 in the Democratic Republic of the Congo (DRC).^39,40 In recent years, cases have increased, possibly related to increasing urbanisation and decreasing population immunity since the end of widespread smallpox vaccination. Occasional human mpox cases were also reported in non-endemic countries before 2022.^41-43

In May 2022, a multi-country outbreak of mpox was reported in regions that are not endemic for mpox, including Australia. This is the first time ongoing human-to-human transmission has occurred in non-endemic regions. 

Sexual contact has been the main driver of the global outbreak. Although anyone can acquire mpox, cases in this outbreak have primarily been among interconnected sexual networks of gay, bisexual and other men who have sex with men (GBMSM).⁴⁴ People at highest risk are GBMSM including transgender and gender-diverse people who have multiple sexual partners, or attend large parties or sex-on-premises venues. However, anyone who comes into close physical contact with someone with mpox can acquire the condition. 

Since 2023, there has been an emergence of mpox cases in DRC and several neighbouring countries, particularly a new clade Ib lineage. In August 2024, the upsurge of mpox was declared a public health emergency of international concern by WHO, with the potential transmission across countries in Africa and possibly outside the continent.⁴⁵

Mpox in Australia

Mpox was first reported in Australia in May 2022. Although case numbers have been generally declining with the commencement of the vaccination program, the global outbreak is still ongoing. In 2024, a resurgence of clade II mpox cases were notified in Australia, with the majority of cases being locally acquired. Official case numbers are likely to be an underestimate, due to under-reporting and asymptomatic cases.

Smallpox and mpox vaccines contain the vaccinia virus, an Orthopoxvirus related to both smallpox and mpox. Vaccines using the vaccinia virus for the prevention of smallpox are effective against mpox. 

Historically, first and second-generation smallpox vaccines were used for population-wide smallpox programs and targeted occupational health-related programs in Australia. These vaccines are no longer in general use in Australia, but the second-generation vaccine containing replication-competent live attenuated vaccinia virus (ACAM2000, Emergent BioSolutions) remains available from the National Medical Stockpile on a request basis.
The currently available vaccine against mpox is the third generation, replication-deficient modified vaccinia Ankara – Bavarian Nordic (MVA-BN) vaccine. The MVA-BN vaccine, known variously as JYNNEOS/Imvamune/Imvanex, is registered for use in the United States, United Kingdom, Canada and other countries for prevention of smallpox and mpox. 

Immunogenicity and effectiveness for primary preventive vaccination (PPV) 

There are no direct data from clinical trials on the effectiveness of MVA-BN against smallpox or mpox, and only post-licensure data on effectiveness against mpox in the 2022 outbreak. Vaccine effectiveness estimates from observational studies ranged from 36% to 86% for a single dose of MVA-BN,^6,46-48 and 66%⁴⁹ to 86%⁶ for a complete 2-dose course in people considered at high risk of mpox.

Indirect evidence for vaccine effectiveness of MVA-BN includes immunogenicity data from previous clinical trials. In these studies, seroconversion rates of after receiving MVA-BN ranged from 71.2% to 100% at 2 weeks after 2 subcutaneous doses.^8,9,11,13-18

Effectiveness after intradermal administration 

Vaccine effectiveness for intradermal administration appears to be comparable to subcutaneous administration, based on indirect immunogenicity data and observational studies. In a phase II trial, 524 participants were randomised to receive a standard (0.5 mL) dose of MVA-BN vaccine subcutaneously or a fractional dose (0.1 mL) intradermally.¹⁵ Peak neutralising antibody titres against the vaccinia virus after 2 doses of intradermal MVA-BN were shown to be non-inferior to titres after 2 doses of subcutaneous MVA-BN. According to a United States jurisdictional case-control study, adjusted vaccine effectiveness for a complete 2-dose course is 80.3% for intradermal administration and 88.9% for subcutaneous administration.⁶  

Duration of immunity

Clinical studies have shown evidence of protection against the vaccinia virus at 2 years after a primary course of the MVA-BN vaccine.¹⁴ In people who had received a primary course of MVA-BN 2 years previously, a booster dose of MVA-BN led to a rapid increase in neutralising antibody titres, which remained elevated at 6 months.⁶

The duration of protection against monkeypox virus infection after 1 primary dose of MVA-BN is currently unknown beyond 4 weeks. The rates of breakthrough infections have remained low in 2-dose vaccinated individuals, with median intervals between vaccination and symptom onset ranging from 3 to 12 months.^50-52 Studies have found higher rates of breakthrough infections in people with HIV, multiple male partners or people with weakened immunity; however, most vaccinated people experience a shorter disease course and milder symptoms than those who have not been vaccinated.⁵³

Vaccine effectiveness for post-exposure preventive vaccination (PEPV)

Vaccination with MVA-BN following exposure to mpox may prevent or attenuate the infection.

Effectiveness for PEPV^54,55 against mpox in the recent outbreak was estimated from 73% to 89% based on limited numbers of vaccinated high-risk contacts.

Transport, storage and handling information varies by jurisdiction due to specific distribution protocols, and is provided by relevant state and territory authorities.

Mpox is a notifiable disease in all states and territories in Australia.

The Communicable Diseases Network of Australia Series of National Guidelines on mpox provides details on:

• current case definitions
• testing recommendations
• classification of high, medium and low risk contacts
• post-exposure preventive measures for contacts

State and territory public health authorities can provide further advice about the public health management of mpox, including management of cases and contacts.

For information about post-exposure vaccination for contacts of mpox cases, see Vaccination after exposure to mpox: post-exposure preventive vaccination (PEPV).

MVA-BN is available for use in Australia under s18A (emergency use provision) of the Therapeutic Goods Act 1989. It is approved for use in adults aged ≥18 years by the United States Food and Drug Administration, United Kingdom Medicines and Healthcare products Regulatory Agency and other regulatory bodies.

ATAGI (the Australian Technical Advisory Group on Immunisation) recommends that people of any age in risk groups receive MVA-BN as primary preventive vaccination. Children can be considered to receive MVA-BN for post-exposure preventive vaccination after a risk–benefit assessment. 

People should talk to their healthcare providers before getting MVA-BN if they have a history of severe allergic reaction to chicken or egg protein.

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