Summary of NACI statement of May 15, 2025: Rapid response concerning updated guidance on the use of Imvamune for the prevention of mpox

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• Overview
• What you need to know

Overview

• On May 15, 2025, the Public Health Agency of Canada (PHAC) released the National Advisory Committee on Immunization’s (NACI) Updated guidance on the use of Imvamune^® for the prevention of mpox. This guidance was developed in collaboration with Canada’s Committee to Advise on Tropical Medicine and Travel (CATMAT), and is based on current evidence and expert opinion.
• NACI last issued guidance on routine Imvamune^® use in May 2024. A re-evaluation was prompted by new changes in global mpox epidemiology, including the emergence of clade I mpox viruses (MPXV), recent effectiveness data, and updated guidance from the World Health Organisation (WHO). In August 2024, the WHO declared mpox a Public Health Emergency of International Concern (PHEIC) following a rise in cases of a novel subclade of mpox (clade Ib) in the Democratic Republic of the Congo and several neighbouring countries.
• NACI continues to strongly recommend that individuals at high risk of mpox should receive two doses of Imvamune^® administered at least 28 days (4 weeks) apart.
• Considering recent epidemiological data, NACI has updated the list of individuals at increased risk of mpox. This list now includes individuals who are travelling to an area with ongoing community transmission of MPXV clade I and anticipate either prolonged close contact (such as sharing accommodation) with people who reside in that area or sexual contact with people who reside in, or spend extended time in, that area. Please see the full NACI statement for more details.
• NACI does not routinely recommend Imvamune^® for healthcare workers, with the exception of vaccination post-exposure. However, two doses of Imvamune^® vaccine may be considered on an individual basis for healthcare workers based on a high risk of frequent exposure.
• NACI strongly recommends that healthcare workers who are travelling internationally to support mpox outbreaks should be vaccinated ahead of deployment.
• NACI continues to recommend that personnel who work in research laboratory settings and who are at high risk of occupational exposure to replicating orthopoxviruses that pose a risk to human health should receive two doses of Imvamune^® administered at least 28 days (4 weeks) apart
• For those who are immunocompetent and have previously received a first- or second-generation live-replicating smallpox vaccine, a single dose of Imvamune^® may be offered. This single Imvamune^® dose should be given at least two years after the latest first- or second-generation live-replicating smallpox vaccine.
• NACI recommends that additional vaccine doses may be offered to personnel working in a research laboratory setting who remain at risk of occupational exposure, with a minimal interval of 2 years.
• The exposure risk is different for personnel working with replicating orthopoxviruses in laboratory settings due to their exposure to potential high concentrations of virus, as well as uncommon routes of exposure. There is no evidence that individuals at high risk in community settings, including immunocompromised populations, require additional vaccine doses at this time.

A PDF version of the Statement is available online on the NACI website and updates to the Canadian Immunization Guide (CIG), Part 4, Smallpox and mpox vaccines chapter will be published in the Canadian Immunization Guide (CIG) as soon as possible. 

What you need to know

• Mpox is a viral disease that typically is self-limited, meaning it resolves on its own without the need for extensive treatment, but can cause more severe disease in some populations such as young children, pregnant women and pregnant people, and individuals who are immunocompromised.
• Mpox clade IIb cases continue to be reported in Canada. Clades refer to distinct genetic lineages of the virus, and to date only one mpox clade Ib case has been reported in Canada and it was travel-related. The greatest burden of disease remains among individuals who self-identify as gay, bisexual, or other men who have sex with men (gbMSM).
• In some other countries, significant mpox outbreaks of clades IIb, Ia, or Ib are ongoing and present elevated risks, therefore the WHO has declared mpox a Public Health Emergency of International Concern (PHEIC).
• In this latest update, NACI has expanded the groups who are recommended to receive mpox vaccine (Imvamune^®). NACI continues to recommend that individuals at high risk of mpox should receive two doses of Imvamune^® 28 days apart. This list includes travelers to areas with ongoing community transmission of MPXV clade I who anticipate prolonged close contact with residents of that area or sexual contact with people who reside in or spend extended time in the area of active transmission.
• Mpox vaccine continues to be supplied by the federal government to provincial and territorial public health programs. There is no private market access to mpox vaccine for purchase by individuals in Canada.
• At this time Imvamune^® is not routinely recommended for healthcare workers. However healthcare workers who work at clinics frequently involved in the diagnosis and management of mpox may be at higher risk and may choose to be vaccinated on a case-by-case basis. In addition, healthcare workers who are travelling internationally to support mpox outbreaks should be vaccinated ahead of deployment.
• With the exception of personnel working in research laboratory settings who remain at ongoing occupational risk, there is no need for additional doses of Imvamune^® for individuals at high risk in community settings, including immunocompromised populations at this time.
• NACI continues to recommend that Imvamune^® should be offered to people who are immunocompromised, pregnant or breastfeeding, if vaccination is recommended based on high-risk criteria. Off-label use in pediatric populations may be considered for those meeting the criteria for pre- or post-exposure vaccination.
• Imvamune^® vaccination can be given concurrently (i.e., same day) or at any time before or after other live or non-live vaccines including COVID-19 vaccines.

NACI will continue to monitor the evolving evidence and will update guidance as needed.

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