Interim guidance on the use of Imvamune® in the context of a routine immunization program

What

• Mpox disease: Mpox is caused by the monkeypox virus (MPXV), a mammalian Orthopoxvirus related to the vaccinia, cowpox, as well as variola (smallpox) viruses. Clinical presentation includes pox-like lesions, often in oral and/or anogenital regions, fever, body aches, back pain, and swollen lymph nodes. Since 2022, mpox has been reported across multiple countries previously non-endemic to MPXV including Canada. For more information on mpox in Canada, please visit Mpox (monkeypox).
• Imvamune® vaccine: Imvamune® is a non-replicating, third-generation smallpox vaccine manufactured by Bavarian Nordic, authorized in Canada for active immunization against smallpox, mpox, and related Orthopoxvirus infections and disease in adults 18 years of age and older determined to be at high risk for mpox exposure. Evidence on Imvamune®vaccine effectiveness (VE) against mpox continues to accumulate; numerous observational studies initiated during active mpox outbreaks since 2022 are reporting high VE against symptomatic mpox. Available clinical and post-marketing safety surveillance data on Imvamune® demonstrates that the vaccine is well-tolerated. The most common adverse events (AEs) reported by adults following 1 and/or 2 doses were non-serious injection-site (e.g., swelling, pain) and systemic (e.g., fatigue, headache) reactions.

Who

NACI makes the following recommendations for public health program and individual decision making:

• Individuals at high risk of mpox should receive two doses of Imvamune® administered at least 28 days (4 weeks) apart.
• Imvamune® vaccination can be given concurrently (i.e., same day) or at any time before or after other live or non-live vaccines.
• Doses should be administered via subcutaneous injection. Dose sparing strategies involving intradermal administration are not recommended in the context of routine immunization.
• Those who have started a primary series with Imvamune®, in whom more than 28 days have passed without receipt of the second dose, should receive the second dose regardless of time since the first dose.
• Those who have previously received smallpox vaccination (e.g., previous generation live-replicating vaccine) and are recommended to receive Imvamune® based on risk factors for mpox should also receive a 2-dose series with a minimum interval of 28 days.
• NACI guidance on the use of Imvamune® in the context of a routine immunization program should be considered interim, and will be re-evaluated once additional evidence emerges. Vaccine eligibility based on increased risk for mpox should be informed by available clinical evidence and ongoing epidemiology. Risk factors may change over time and should be assessed by local and/or provincial/territorial public health.
• At this time, individuals considered at high risk of mpox in Canada include:
  1. Men who have sex with men (MSM) who meet one or more of the following criteria:
     1. have more than one partner
     2. are in a relationship where at least one of the partners has other sexual partners
     3. have had a confirmed sexually transmitted infection acquired in the last year
     4. have engaged in sexual contact in sex-on-premises venues.
  2. Sexual partners of individuals who meet the criteria above.
  3. Sex workers (regardless of gender, sex assigned at birth, or sexual orientation).
  4. Staff or volunteers in sex-on-premises venues where workers may have contact with fomites potentially contaminated with mpox.
  5. Those who engage in sex tourism (regardless of gender, sex assigned at birth, or sexual orientation).
  6. Individuals who anticipate experiencing any of the above scenarios.
• NACI continues to recommend the use of Imvamune® as a 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.
• A post-exposure vaccine dose should be offered as soon as possible, preferably within 4 days of last exposure, but can be considered up to 14 days from last exposure.
• After 28 days, a second dose should be offered if MPVX infection did not develop, regardless of ongoing exposure status.
• Individuals with previous or active MPXV infection should not be offered Imvamune®
• Off-label use in pediatric populations is recommended for those meeting the criteria for post-exposure vaccination, and may be offered at their clinician's discretion.
• Imvamune® vaccination can be given concurrently (i.e., same day) or at any time before or after other live or non-live vaccines.

MSM: Man or Two-Spirit identifying individual who has sex with another person who identifies as a man, including but not limited to individuals who self-identify as trans-gender, cis-gender, Two-Spirit, gender-queer, intersex, and non-binary.

Why

• While the incidence of mpox in Canada has significantly declined since the fall of 2022, mpox remains an important public health concern with the potential for future resurgence.
• After NACI provided guidance for Imvamune® pre-exposure vaccination, most Canadian jurisdictions offered the vaccine to populations/groups consistent with NACI guidance. Across Canada, individuals self-identifying as gay, bisexual, or other men who have sex with men (gbMSM) who are considered at high risk of mpox exposure (e.g., multiple sex partners, recent sexually transmitted infection; STI) are eligible for Imvamune® pre-exposure vaccination; however, specified risk factors and eligibility for other groups (e.g., sex workers) varies by jurisdiction.
• Up to December 10, 2023, approximately 143,471 vaccine doses were administered in Canada, primarily in Ontario (n=52,747), Quebec (n=46,870), and British Columbia (n=30,168). Specifically, 103,572 people were vaccinated against mpox with at least one dose of Imvamune® in response to this outbreak, while 39,631 people were vaccinated with two dosesFootnote1.
• Due to evolving mpox epidemiology in Canada and emerging evidence on VE of Imvamune®, Canadian provinces and territories, as well as several stakeholders, have indicated the need for national guidance on pre-exposure vaccination outside the context of an ongoing mpox outbreak. This included identification of priority populations for pre-exposure vaccination and guidance on a recommended vaccine schedule in the context of a focused routine immunization program.