Measles Memo from the Ministry of Health, June 2025

Dear Colleagues,

The purpose of this memo is to provide you with some updates regarding measles outbreak preparedness and response.

As you are likely aware, like many parts of the world, Ontario is experiencing a large measles outbreak, with 2,009 outbreak cases reported between October 18, 2024 and June 3, 2025. 1,965 of these casesare past the period of communicability. Approximately 96% of cases in Ontario linked to this outbreak are among individuals who are unvaccinated or of unknown immunization status. Although outbreak cases have occurred to date in 19 public health units, the outbreak continues to be concentrated predominantly in southwestern Ontario within communities with historically low rates of immunization.

Ensuring high measles vaccine coverage is a key component of preventing and responding to measlesoutbreaks. Two doses of measles-containing vaccine have an efficacy of nearly 100%, and additional booster doses are not recommended.

As of May 2025, the following public health units have implemented an outbreak immunization strategyin affected regions and communities with active measles cases and where the risk of exposure in the community is higher:

  • Chatham-Kent
  • Grand Erie
  • Grey Bruce
  • Huron Perth
  • Lambton
  • Middlesex-London
  • Waterloo
  • Wellington-Dufferin-Guelph
  • Windsor-Essex
  • Southwestern

The outbreak immunization strategy is recommended for individuals who live, work, travel (e.g., familyvisit), worship, or spend time in these Public Health Unit jurisdictions.

  • Infants (six to 11 months): Should receive one dose of the measles, mumps, rubella (MMR) Two additional doses are required after the age of one year.
  • Children (one to four years): Children who have received their first dose of MMR vaccine are encouraged to receive a second dose as soon as possible (at a minimum of four weeks from the first dose).
  • Adults (18+ years) born on or after 1970: A second dose of MMR vaccine (for those who have not already received 2 doses) is recommended.

Health care providers in other public health unit jurisdictions (i.e., those not listed above) should be aware of the outbreak immunization recommendations to ensure those planning to visit/travel to affected regions are vaccinated appropriately.

Ensuring high measles vaccine coverage in all parts of the province is a key element of preventing further spread of the current outbreak. Providers in other parts of the province (not listed above) shouldcontinue to offer routine or catch-up immunizations as per Ontario’s Publicly Funded Immunization Schedules, especially for children who may have missed vaccines due to the COVID-19 pandemic and for adults born after 1970 with unknown immunization status. Please see Public Health Ontario’s Routine and Outbreak-related Measles Immunization Schedules for a quick summary .

As summer represents a time of increased travel, ensuring measles protection before travel is also important. Adults born on/after 1970 and all children should be protected with 2 doses of measles-containing vaccine prior to travel outside of Canada. Infants 6 to 11 months of age are also recommended a dose of MMR vaccine, similar to the current outbreak strategy.

Health care providers should ensure all staff are immunized and have immunization records or laboratory results with proof of immunity readily available.

MMRV vaccine is publicly funded routinely for individuals 4 to 6 years of age and for catch-upimmunizations for individuals 7 to 12 years of age. While MMRV can be used for outbreak and measles contact management purposes, we ask that MMRV be used primarily for routine or catch-up immunizations.

If an individual’s immunization records are unavailable, getting immunized with a measles-containing vaccine is generally preferable to ordering a laboratory (serology) test to determine immune status.There is no harm in giving measles-containing vaccine to an individual who is already immune.

Please refer to the attached FAQ for further recommendations on managing measles in health care settings.

FAQ in English, click here.

FAQ in French, click here.

In health care settings, appropriate infection prevention and control (IPAC) practices and processes play a critical role in minimizing or reducing measles exposures and transmission. For additional IPAC support in clinical settings, health care providers in impacted regions may also connect with their local IPAC Hub. To locate your local IPAC Hub please contact IPACHubs@ontario.ca.

Health care providers, in collaboration with public health units, should assess immunization status andsupport vaccination efforts of International Agriculture Workers (IAW).

The ministry continues to meet with the affected public health units and Public Health Ontario.

Additional information:

Thank you for your continued efforts in ensuring Ontarians are protected from vaccine preventable diseases.

Sincerely,
Dr. Kieran Michael Moore, MD, CCFP(EM), FCFP, MPH, DTM&H, FRCPC, FCAHS
Chief Medical Officer of Health and Assistant Deputy Minister

C: Elizabeth Walker, Executive Lead, Office of the Chief Medical Officer of Health Dr. DanielWarshafsky, Associate Chief Medical Officer of Health, Office of the Chief Medical Officer of Health

Michael Sherar, President and Chief Executive Officer, Public Health Ontario