Ontario is experiencing its most significant measles outbreak since the 1990s, with 177 confirmed cases reported between October 2024 and February 2025, according to provincial health officials [1].

The Southwestern Public Health Unit, covering St. Thomas, Oxford County, and Elgin County, has recorded 115 cases since October 28, with 89 of those occurring in 2025 alone [1][2]. Eighteen people have been hospitalized across Ontario, including one requiring intensive care.

Dr. Ninh Tran, medical officer of health for the Southwestern Public Health Unit, notes the outbreak's severity: "It's so infectious that any pockets of areas or people who aren't immunized, it will go right through it." The virus has a 90% transmission rate among unvaccinated individuals [3].

The outbreak has spread beyond Ontario's borders, with 30 cases reported in Quebec and five in Manitoba. British Columbia has identified two cases, both linked to international travel [1].

Provincial vaccination rates have fluctuated significantly. While reaching 94% coverage among seven-year-olds in 2013-14, rates dropped to 67.4% during the COVID-19 pandemic, recently recovering to 70.4% [4]. However, the Southwestern Public Health Unit maintains higher rates, currently approaching 95%.

Public health officials have launched new initiatives, including a measles immunization clinic for six- to 11-month-olds, marking a departure from standard vaccination schedules [2]. The MMR (measles, mumps, rubella) vaccine remains 99% effective in preventing infection.

Health authorities are urging symptomatic individuals to stay home and contact healthcare providers by phone rather than visiting facilities, as many exposures have occurred in healthcare settings [3].