Measles Resurgence in Ontario: Health Officials Urge Vaccination as Cases Reach Decade High

Ontario is currently experiencing a significant resurgence of measles, with the number of confirmed cases reaching levels not seen in over a decade. As of March 12, 2025, the province has reported a total of 350 cases since October 2024, including 31 hospitalizations.

The outbreak has primarily affected unvaccinated individuals, with over 96% of cases occurring among those who are unimmunized or have unknown immunization status. The majority of these cases are concentrated in southwestern Ontario. ​

Dr. Kieran Moore, Ontario’s Chief Medical Officer of Health, emphasized the importance of vaccination in curbing the spread of measles:​

“​Vaccination is the most effective way to limit the spread of measles and protect yourself and your loved ones.” ​

The measles, mumps, and rubella (MMR) vaccine has been in use for over 50 years and is considered one of the safest and most effective vaccines available. Children who receive two doses are nearly 100% protected against measles, with one dose providing up to 95% protection. ​

The current outbreak is part of a broader national trend. Canada has recorded 227 measles cases as of March 6, 2025, surpassing the total number of cases reported in all of 2024. These cases are predominantly among unvaccinated or under-vaccinated children exposed in community settings such as social events, daycares, schools, and healthcare facilities.

Dr. Theresa Tam, Canada’s Chief Public Health Officer, expressed concern over the rising numbers:​

“​As we move through spring break travel season, I am concerned that the global rise in measles cases, combined with declining vaccination rates among school-aged children in Canada, could lead to more illness and more community transmission.” ​

Measles is highly contagious and can lead to serious health complications, including pneumonia, brain inflammation, and, in rare cases, death. The virus spreads through the air when an infected person coughs or sneezes and can remain infectious on surfaces for several hours. ​

To prevent further spread, health officials are urging individuals to ensure they are up to date with their vaccinations. Children should receive their first dose of the MMR vaccine at 12 months and a second dose between four to six years of age. Adults born in 1970 or later should also verify their immunization status and receive two doses if necessary. ​

In light of the outbreak, public health units across Ontario are working diligently to contain the spread, conducting contact tracing, and providing immunization clinics. Residents are encouraged to contact their healthcare providers or local public health units if they are uncertain about their immunization status or require vaccination. ​

Maintaining high vaccination coverage is essential to protect communities from measles outbreaks. Health officials continue to stress the importance of immunization in safeguarding public health and preventing the resurgence of vaccine-preventable diseases.​