Public health risk assessment: Measles in Canada

Assessment completed: April 24, 2025 (with data as of April 22, 2025)

On this page

• Reason for assessment
• Risk question
• Risk statement
• Scope and contextual considerations
• Risk assessment summary
• Future risk
• Proposed actions for public health authorities
  • Public health interventions: Prevention and response
  • Surveillance and reporting
  • Risk communication
  • Guidance
  • Laboratory activities
• Acknowledgements
• Footnotes

Reason for assessment

Since the March 2024 rapid risk assessment Measles in Canada, public health implications, travel-associated measles introductions have led to ongoing transmission within Canada. In October 2024, such an introduction initiated a multi-jurisdictional outbreak in communities with low immunity to measles and has become the largest measles outbreak in Canada since measles elimination status was achieved in 1998. Concurrently, additional measles outbreaks have been occurring in populations with higher levels of immunity to measles, indicating gaps in population immunity. This risk assessment considers the current measles outbreaks in Canada to identify public health implications for Canada and determine appropriate public health actions.

Risk question

What is the likelihood of prolonged measles transmission in the next six months (mid-April to mid-October 2025) from the current outbreaks in Canada, and the resulting impact from such transmission?

Risk statement

The overall risk of measles for the population in Canada is moderate, given prolonged transmission among communities with low immunity to measles^{Footnote a}, potentially serious impacts on those communities, and burden on public health resources. Individuals in Canada who are not immune via vaccination or prior infection are at increased risk of infection and serious outcomes if exposed, as measles is highly transmissible and potentially severe.

The likelihood of prolonged transmission in the next six months is moderate-high, driven by the outbreak involving communities with low immunity to measles. The most likely spread scenario is one where transmission will continue within socially connected communities with low immunity to measles, as social events and mobility among and between these communities will facilitate introductions across multiple provinces and territories. Although periodic introductions into populations with higher levels of immunity to measles in Canada are expected to result in limited chains of transmission, exposure events in higher-risk settings, such as healthcare facilities or schools, are of concern.

There is a moderate level of uncertainty in the likelihood of this scenario occurring, due to unpredictable timing of introductions from the current outbreaks into other communities, variation in size of communities into which measles is introduced and their level of susceptibility, as well as the role that preventative interventions could play in reducing transmission in these communities. Canada has been free of endemic^{Footnote b} measles since 1998 however, uninterrupted transmission from current outbreaks places Canada at risk of losing measles elimination status if vaccination efforts and non-pharmaceutical public health measures are unable to interrupt transmission.

At the individual-level, the impact of infection with measles is expected to be minor for vaccinated individuals, moderate for unvaccinated individuals, including unvaccinated children aged 1 to 5, and moderate to major for individuals at higher risk of severe disease, including infants, immunocompromised individuals, and unvaccinated pregnant individuals.

The population-level impact from the most likely scenario is expected to be moderate, with moderate uncertainty and is driven by population health impacts in affected communities and high demand on public health resources required for outbreak management in multiple regions of Canada. Diverting public health resources for outbreak management (i.e., vaccination, isolation, case management, contact tracing, and public communication) could have temporary negative impacts on other public health functions, particularly in regions with limited capacity to respond. Multiple hospitalizations over a short period of time could lead to intensive resource demands within healthcare facilities due to needs for case isolation to ensure infection prevention and control standards.

Scope and contextual considerations

The overall risk question concerns the likelihood of prolonged transmission from ongoing outbreaks in Canada and the related impacts. As a result, the likelihood and impact of newly imported measles cases is out of scope. The Rapid risk assessment: Measles in Canada, public health implications in 2024 addressed individual-level impacts from measles (e.g., morbidity and mortality) and remain relevant, therefore these are not re-estimated in the current risk assessment.

Risk assessment summary

Future risk

Canada is currently facing a multi-jurisdictional measles outbreak that is the largest since the virus was declared eliminated in 1998. If the current chain of transmission continues beyond October 2025, Canada could lose its elimination status. Prolonged transmission reflects gaps in population immunity, often due to limited access to or uptake of vaccines, and can lead to preventable illness, long-term complications, and death, especially in vulnerable groups.

Persistent under-vaccination in affected communities increases the risk of endemic transmission, future domestic outbreaks, and could lead to international spread. Even if high immunity is reached in communities affected by the current outbreak, continued importation of measles due to global and domestic vaccination declines, international travel, and uncertain uptake of public health measures could trigger new outbreaks.

Though vaccination is the most effective public health intervention, some individuals choose not to be vaccinated for personal reasons, despite having access to accurate information. In these circumstances, a two-pronged approach may be required that is to promote and facilitate vaccination among those willing to receive it, and for those who choose to remain unvaccinated promoting uptake of public health measures such as advising individuals to stay home when ill and seek timely medical care. This approach balances respect for individual autonomy with the need to protect public health and reduce the risk of ongoing transmission.

In addition, slow recovery from pandemic-related disruptions to vaccination schedules, mistrust in public health measures, and mis- and disinformation present an ongoing challenge for public health to control measles and other vaccine-preventable disease outbreaks.

As many countries experience large and complex outbreaks, communication and collaboration with international partners will be increasingly important. This will help countries share information and coordinate mitigation strategies to reduce the risk of importation and exportation, and hinges on shared commitment to evidence-based public health policies. Strengthening trust in accurate and reliable sources of public health information and building relationships with under-vaccinated communities in collaboration with community leaders could be helpful in overcoming these challenges.

Proposed actions for public health authorities

Measles is a highly contagious vaccine-preventable disease. Due to increases in measles activity nationally and globally, it is important to collaborate and coordinate with partners (including community and Indigenous partners, and all levels of government) at all stages of preparedness, planning and response. A continued multipronged approach is essential to prevent and manage outbreaks and community transmission.

Recommendations provided below are based on findings of this risk assessment and include current efforts by local, provincial, and federal public health partners. Additional strategies are included for consideration by jurisdictions according to their local epidemiology, policies, resources, and priorities. Due to the current level of uncertainty associated with the trajectory of measles outbreaks in Canada, it is important that the public health response be proportionate to the risk.

Public health interventions: Prevention and response

• Prepare to manage an increased volume of cases and contacts (e.g., adequate isolation capability, early detection, and management of measles cases and contacts including contact tracing and management, adequate laboratory testing capacity, and supply and availability of vaccines and immunoglobulins). Consider establishing service corridors and care pathways (e.g., calling ahead to alert a facility an incoming patient may have measles; measles screening in impacted areas to reduce healthcare setting exposures; designated measles centres to contain exposure risk across facilities).
• Continue to address existing gaps in measles immunity; increase and maintain high routine measles vaccination coverage while considering vaccination campaigns targeting at-risk settings and populations (e.g., offering vaccines for children under the age of one year and accelerated second doses for children living in outbreak-affected communities). In addition, explore mechanisms to reach un/under-vaccinated communities at risk, including vaccine hesitant communities.
• Consider activities to enhance awareness and education of health professionals on early detection and management of measles cases and contacts. Additionally, encourage healthcare providers to continue to inform their patients, especially those intending to travel nationally and internationally (see the Global Measles travel health notice) about the importance of being up to date with measles vaccination and advise patients to follow public health guidance if they are exposed or become infected (e.g., seek timely care and if symptomatic, isolate to prevent further transmission).

Surveillance and reporting

• Continue to collect, analyze, and share measles case data, measles vaccination coverage data and seroprevalence data to monitor population immunity, identify areas with higher susceptibility to measles outbreaks and to inform local, provincial/territorial and federal public health response.

Risk communication

• Develop targeted educational and awareness messaging for populations at increased risk using tailored outreach mechanisms (e.g., using behavioural science, supporting community-led solutions, etc.) while continuing with broad communication on the current measles situation and how to prevent infection. This could include encouraging vaccination for those who are willing, and the adoption of other public health measures (e.g., including staying home while sick and seeking care promptly) for those who are not.
• Collaborate with community leaders and partners involved with populations at increased risk to provide evidence-based information including content identifying risks associated with mis- and disinformation regarding measles, vaccines and treatments.

Guidance

Refer to the recommendations provided within PHAC's Process for contact management for measles cases communicable during air travel and the forthcoming update to Guidance for the public health management of measles cases, contacts and outbreaks in Canada (May 2025), to assist in the management of measles cases, contacts, and outbreaks.

Laboratory activities

• Continue collecting viral specimens for measles diagnostic and confirmatory testing, which enables viral genotyping necessary for investigation of the source of infection and for surveillance to monitor measles elimination status.

Technical annex: For further risk assessment details, including technical annex, please contact rap-per@phac-aspc.gc.ca.

Acknowledgements

Completed by the Public Health Agency of Canada in collaboration with partners from:

• Health Canada
• Indigenous Services Canada
• British Columbia Centre for Disease Control
• Government of Northwest Territories
• Government of Saskatchewan
• Public Health Ontario