Mpox (monkeypox) resources for health care professionals

Overview

Mpox (formerly known as monkeypox) is an infectious disease caused by the monkeypox virus, typically transmitted from animals to humans, that causes a disease with symptoms similar to, but less severe, than smallpox.

Since May 2022, numerous cases and outbreaks of mpox have been reported across several European, American, African, Western Pacific, Eastern Mediterranean, and South-East Asian countries, where mpox has not been typically found and where there are no identified associations with travel to mpox endemic countries.

The virus that causes mpox is distinguished by two separate genetic clades:

• Clade I
• Clade II

Clade I

Sub-clade Ia is endemic to Central Africa and causes more severe illness and deaths than clade II. Sub-clade Ib emerged in the Democratic Republic of Congo (DRC) in 2023 and is spreading through direct contact, primarily through heterosexual networks.

Clade II

This clade is endemic to West Africa and is associated with less severe illness and deaths than clade I. Sub-clade IIb was responsible for the 2022 global mpox outbreak that primarily affected adults who identified as men who have sex with other men.

Ontario continues to monitor for cases of mpox, (clade I and II), and is working collaboratively with partners in Ontario and nationally.

Symptoms

Mpox has a broad range of clinical presentations with common symptoms that include:

• fever
• new rash/lesions in the mouth, genital or peri-anal region
• rectal pain
• lymphadenopathy

Mild and subclinical infections are suspected to be the cause of ongoing transmission. Clinicians should keep mpox on their differential diagnosis and have a low threshold to test in risk groups with compatible signs and symptoms. Mpox is typically mild and self-limiting, with most people recovering within 2 to 4 weeks. However, severe illness can occur in some individuals.

Transmission

The main route of mpox virus transmission is:

• direct close contact (skin-to-skin)
• direct contact with skin lesions/scabs, bodily fluids, and mucus membranes in the mouth, tongue, and genitalia

Other less common routes of transmission include:

• respiratory transmission
• contact with materials contaminated with monkeypox virus (such as contaminated bedding, linens, towels, lesion dressings or needles)
• close but non-direct contact (non-sexual household contacts, for example) can occur

These less common routes of transmission have not been observed in Ontario data and investigations to date.

On June 16, 2022, mpox was designated as a Disease of Public Health Significance (DOPHS) requiring the reporting of mpox cases (see Appendix 1: Case Definitions and Disease Specific Information, Disease: Smallpox and other Orthopoxviruses including Monkeypox) directly to the local medical officer of health in accordance with the reporting requirements in the Health Protection and Promotion Act, as per routine disease processes.

Vaccination

Imvamune® is authorized in Canada for protection against mpox. Imvamune® is a third generation smallpox vaccine. It is a two-dose series, given 28 days apart. Booster doses are not recommended.

Imvamune® should be considered for the following:

• Pre-exposure vaccination  – when Imvamune® is administered before known exposure to the virus for individuals at high risk of mpox exposure.
• Post-exposure vaccination  – when Imvamune® is administered for individuals who have had a high-risk exposure to a probable or confirmed case of mpox, or within a setting where transmission is happening.

Pre-exposure vaccination for high-risk individuals

The following individuals are considered at high risk for mpox exposure and are eligible for pre-exposure vaccination:

• Two-Spirit, non-binary, transgender, cisgender, intersex, or gender-queer individuals who self-identify as belonging to the gay, bisexual, pansexual and other men who have sex with men (gbMSM) community AND who meet one or more of the following:
  • have more than one partner
  • are in a relationship where at least one of the partners has other sexual partners
  • have had a confirmed sexually transmitted infection within the last year
  • have attended venues for sexual contact (for example, bath houses, sex clubs)
  • have had anonymous sex recently (for example, using hookup apps)
• sexual partners of individuals who meet the criteria above
• sex workers (regardless of gender, sex assigned at birth, or sexual orientation) or who are a sexual contact of an individual who engages in sex work
• staff or volunteers in sex-on-premises venues where workers may have contact with surfaces or objects that may be contaminated with mpox
• individuals who engage in sex tourism ^{footnote 1[1]} (regardless of gender, sex assigned at birth, or sexual orientation)
• individuals who anticipate experiencing any of the above scenarios
• research laboratory employees working directly with replicating Ortho poxviruses

Household contacts of those identified for pre-exposure vaccination eligibility above who are moderately to severely immunocompromised or who are pregnant may be at higher risk for severe illness from mpox infection and may be considered for pre-exposure vaccination. Individuals who meet this criteria should contact their health care provider, or their local public health unit, for more information.

Post-exposure vaccination

The National Immunization Advisory Committee (NACI) continues to recommend the use of Imvamune® as post-exposure vaccination (also known and referred to as post-exposure prophylaxis) to individuals who have had high risk exposure(s) to a probable or confirmed case of mpox, or within a setting where transmission is happening, if they have not received both doses of pre-exposure vaccination.

The provision of Imvamune® for post-exposure vaccination requires an assessment of the risk of exposure by the local public health unit.

Dosage

• The first dose should be offered as soon as possible, ideally within 4 days (up to 14 days) from the date of the last exposure to individuals who are a high-risk contact of a confirmed or probable case of mpox.
• A second dose should be offered 28 days after the first dose if mpox infection did not develop, regardless of ongoing exposure status.

If the window for post-exposure is missed (for example, more than 14 days after exposure) consider administration of Imvamune® as pre-exposure vaccination.

Optimal protection

It is important to receive both doses for optimal protection. Recent studies have shown vaccine effectiveness to be up to 83% for patients with a 2-dose vaccine series. Recent Ontario data has shown that vaccine effectiveness for persons who have received at least one dose of Imvamune® was 58%.

Even though vaccination is not 100% effective, as with vaccines in general, vaccinated individuals are expected to be less likely to report severe symptoms and to require hospitalization than persons who have not been vaccinated if they become infected. As such, clinicians should continue to promote first and second dose vaccination.

As per NACI, booster doses are not recommended at this time.

Co-administration of Imvamune®

As per NACI, Imvamune® can be given concurrently (for example, on the same day) or at any time before or after other live or non-live vaccines.

People travelling to areas with mpox clade I and II

People without other risk factors per above are not eligible to receive Imvamune based solely on travel. At this time, those travelling to areas where there are increased cases of mpox are encouraged to practice enhanced health precautions as per the Government of Canada. Individuals who are eligible for vaccine per the above high-risk criteria are encouraged to be vaccinated prior to travel.

Tecovirmat antiviral

The anti-viral drug tecovirimat (TPoxx®) is a medication authorized for smallpox that inhibits the production of an orthopoxviral envelope protein required for cell-to-cell viral dissemination.

The efficacy of TPoxx® in the treatment of mpox has not been formally evaluated in clinical trials, but use is reasonable on the basis of its efficacy against smallpox, animal data, and unpublished data in humans with mpox.

TPoxx® is available for mpox patients who are severely ill due to mpox infection or at high risk of experiencing severe disease. A licensed health care professional may request this drug for eligible patients based on their clinical judgement for treating severe mpox infections.

To request Tpoxx® refer to the Mpox Antiviral Guidance for Health Care Providers.

Mpox in animals

Some animals can become infected with mpox, including:

• rodents (such as rats, mice, hamsters, gerbils, squirrels, chipmunks)
• rabbits
• hedgehogs
• opossums
• non-human primates (such as monkeys)

Mpox has been reported on a dog that had close contact with its infected owners. As such, precautions should be taken to prevent exposure of the virus to domestic and wild mammals.

Veterinarians that suspect an animal has been infected with mpox should call the Ontario Ministry of Agriculture, Food and Agribusiness at 1-877-424-1300 to discuss management plans.

Resources for health care providers