Mpox (monkeypox)

What is it?

Mpox is a viral zoonosis (an infection spread from animals to humans). It is caused by a virus that belongs to the Orthopoxvirus genus (which also causes the variola virus responsible for smallpox disease and the vaccinia virus, which is used in smallpox vaccines). Mpox was first discovered in 1958 and there have been small outbreaks since, predominantly in Western and Central Africa. Since the eradication of smallpox in 1980, mpox has become the most important orthopoxvirus affecting humans, however, causes less severe disease than smallpox.

What to look for

The incubation period of mpox is usually 7-14 days, but can be as short as 5 days or as long as 21 days. The initial symptoms include fever, headache, backache and muscle aches, fatigue and lymphadenopathy. Lymphadenopathy in this early phase is a key feature of mpox.

1-3 days following the beginning of fever, a rash may develop, often beginning on the mouth and face, and then spreading to other areas of the body. The face is involved in 95% infections, followed by the palms of the hands and soles of the feed (75%). Oral mucous membranes are involved in 70% of cases, and involvement of the genitalia is also common (30%).

The rash is initially characterised as being erythematous (reddened) and macular (flat), which then develops papular features (raised areas) and turns into well-demarcated pustules and vesicles. These then dry into crusts and fall off. The number of lesions is highly variable, ranging from a couple to over a thousand.

The infection is usually self-limiting with symptoms lasting from 2-4 weeks. Complications can include secondary infection such as cellulitis, sepsis, infection of the cornea (which can be threaten vision), bronchopneumonia and encephalitis. The case fatality ratio is between 3-6%. More severe illness can occur in immunocompromised people.

How is it transmitted?

Mpox is spread via either animal-to-human transmission (zoonotic) or human-to-human transmission.

Zoonotic transmission involves direct contact with the bodily fluids, blood, or lesions (cutaneous or mucosal) of infected animals. This is most common for people living near or within forest areas with exposure to infected animals.

Human-to-human transmission involves close contact with respiratory secretions, the skin lesions of an infected person, or a contaminated objects such as linen or clothing. Droplet particle transmission requires prolonged face-to-face exposure, placing household contacts at highest risk. This can be minimised by isolating away from other members of the household.

Healthcare workers caring for individuals with mpox must undertake infection control precautions and handling of laboratory specimens should be by suitably trained staff.

Epidemiology

Mpox is very common in West and Central Africa, often in areas with tropical rainforests. However, there are currently outbreaks in many other countries across the globe including Australia and parts of Europe and the United Kingdom.

Vaccines

The vaccinia virus is a poxvirus related to smallpox and mpox and is contained in smallpox vaccines. Historically, smallpox vaccines have been used in the prevention of smallpox infection, however, they are also likely to be effective against mpox.

There are two types of smallpox vaccines available for use in Australia for the prevention of mpox:

• ACAM2000™ – 2nd generation, live-attenuated vaccine
• JYNNEOS® – 3rd generation, non-replicating vaccine

Recommendations

Either vaccine can be administered subcutaneously as either primary preventative vaccination (PPV) or post-exposure preventative vaccination (PEPV) based on an individual risk-benefit assessment. ATAGI preferentially recommends JYNNEOS® vaccine due to the ease of administration and decreased likelihood of side effects.

For PPV, administering JYNNEOS® via the intradermal route can be considered in all eligible populations to maximise vaccine supply. In circumstances where vaccine supply is limited severely immunocompromised individuals should be prioritised over other eligible groups such as healthcare workers to receive their second dose of JYNNEOS® (ACAM2000™  is contraindicated in this population). Intradermal vaccination is currently recommended for PPV only.

For PEPV, vaccination within 4 days is recommended to provide optimal protection against the development of mpox infection. Vaccination between 4-14 days following exposure may lessen the severity of disease.

Vaccination is currently recommended for the following groups:

• those who are categorised by public health authorities as a high-risk mpox contact in the previous 14 days (PEPV)
• gay, bisexual, and other men, non-binary individuals assigned male at birth, trans men who have sex with men (including cis and trans men) who are the highest risk of infection with mpox. Markers indicating increased risk of infection include:
  • those living with HIV
  • recent history of multiple sexual partners, including group sex or sex on licensed premises
  • other markers including recent sexually transmitted disease or on HIV PrEP due to number of partners
  • recommendations from sexual health clinics
• sex workers, particularly those with clients who belong to high-risk groups
• anyone in the above categories planning to travel to a country experiencing a mpox outbreak (immunisation is recommended 4-6 weeks prior to travelling)
• anyone at greater risk of poorer outcomes due to mpox infection, such as those with severe immunocompromise
• immunisation providers who are administering ACAM2000™.

Individuals who have a history of confirmed mpox infection should defer vaccination in the short-medium term after recovery due to the immunity gained from natural infection.

Precautions

Vaccination with JYNNEOS® can be considered in children aged < 18 years where the benefits of vaccination outweigh the risks of disease. Despite limited safety data, there are no theoretical safety concerns surrounding the administration of JYNNEOS® in pregnant or breastfeeding women.

Individuals receiving ACAM2000™ as PPV should consider an interval of 4 weeks between vaccination and administration of COVID-19 vaccines due to the rare risk of myocarditis/pericarditis.

Individuals with a history of keloid scarring are not recommended to receive JYNNEOS® via the intradermal route, with subcutaneous being preferred.

Contraindications

Anyone with a history of anaphylaxis to a previous dose of the vaccine to be administered or anaphylaxis to a component of the vaccine to be administered should not be vaccinated.  Due to the risk of vaccine associated disease, ACAM2000™ is contraindicated for those with immunocompromise or those who are pregnant.

Individuals with active eczema, atopic dermatitis or other exfoliative skin conditions should not receive ACAM2000™ due to the risk of developing eczema vaccinatum (a reaction to smallpox vaccination experienced by people with eczema/atopic dermatitis resulting in a severe rash and systemic illness).

*an interval longer than 28 days is acceptable. If supply is limited, severely immunocompromised individuals should be prioritised to receive their 2nd dose as close to 28 days from dose 1 as possible.
§ Using alternate routes of vaccine delivering to complete a primary course is acceptable (eg, intradermal for dose 1 and subcutaneous for dose 2)
€ Intradermal administration is an alternate route of vaccination for pre-exposure prophylaxis. It is not preferred for the first dose of post-exposure prophylaxis and is NOT recommended in people with severe immunocompromise
£ Vaccination providers administering intradermally should ensure that they are appropriately trained in intradermal technique. Where a dose of intradermal vaccine is inadvertently administered subcutaneously, a repeat dose of 0.5ml should be administered subcutaneously as soon as possible to ensure that the vaccinee receives an appropriate level of protection
^ Percutaneous administration involves using a bifurcated needle and scarification technique requiring specialised training and accreditation
# for full aftercare instructions, refer the product information
¥ ACAM2000 is a live-attenuated vaccine and therefore as outlined above, it’s use is contraindicated in some patient groups. For a full list of contraindications and precautions refer to the ATAGI clinical guidance on vaccination against Mpox.

Following vaccination

Individuals receiving ACAM2000™ should be advised that 2-5 days after vaccination a papule will form at the injection site. This will progress to a vesicle (blister) then pustule (blister with pus) before scabbing and forming a permanent pitted scar. Individuals are recommended to cover the injection site with a gauze bandage secured with adhesive tape until scabbing occurs, noting that the wound is infectious until the wound dries up.

Common systemic side effects following vaccination with either vaccine include muscle aches, headache, fatigue and nausea. Localised side effects can include injection site itch, pain redness and swelling (and permanent scarring following ACAM2000™.

ACAM2000™ is also associated with a risk of myocarditis and pericarditis as well as other serious side effects noted here.

Resources

Victorian program information

• Victorian Department of Health: Mpox [includes information on where to access vaccines]

Other resources

• ATAGI clinical guidance on vaccination against mpox
• Australian Government Department of Health and Aged Care: Mpox resources
• Mpox virus infection: CDNA National Guidelines for Public Health Units
• Better Health Channel: Mpox