NACI Rapid Response - Interim guidance on the use of Imvamune® in the context of monkeypox outbreaks in Canada

On June 10, 2022, the Public Health Agency of Canada (PHAC) released interim guidance from the National Advisory Committee on Immunization (NACI) on the use of Imvamune® in the context of monkeypox outbreaks in Canada. This guidance is based on current evidence and NACI's expert opinion.

Canada first declared cases of monkeypox on May 19, 2022, and continues to experience an outbreak with 81 confirmed cases as of June 7, 2022.

Imvamune® is an orthopoxvirus vaccine made by Bavarian Nordic that is authorized by Health Canada for immunization against smallpox, monkeypox and other pox viruses in adults 18 years of age and older who are at high risk of exposure.

In the context of the rapidly evolving monkeypox outbreak, NACI has provided options for the use of the Imvamune® vaccine for post-exposure prophylaxis against monkeypox. Post-exposure prophylaxis is when a medical intervention is taken to prevent disease after a possible exposure. In developing these options, NACI reviewed data on the current status of the monkeypox outbreak and evidence on the safety and protection offered by the Imvamune® vaccine.

For post-exposure prophylaxis (PEP), NACI recommends:

• A single dose of the Imvamune® vaccine may be offered to people with high risk exposures (to be defined by PHAC) of a probable or confirmed case of monkeypox, or within a setting where transmission is happening. This dose should be offered as soon as possible, ideally within 4 days of exposure, but may be considered up to 14 days since last exposure. PEP should not be offered to people who have current monkeypox infection.
• A second dose may be offered after 28 days if an assessment indicates an ongoing risk of exposure.
• People with a history of myocarditis and/or pericarditis linked to a previous dose of an orthopoxvirus vaccine should discuss the benefits and risks of receiving Imvamune® with their doctor.

NACI recommends that Imvamune® be given at least 4 weeks before or after an mRNA COVID-19 vaccine, if possible. However, Imvamune® vaccination should not be delayed due to the receipt of an mRNA COVID-19 vaccine.

Unrelated to the current monkeypox outbreak, NACI has also provided guidance on the use of Imvamune® for pre-exposure prophylaxis in routine laboratory research settings where replicating orthopoxviruses are studied.