Medical Advisory: Updated Areas of Increased Measles Risk and Vaccination Recommendation

Ontario continues to experience ongoing measles transmission. As of May 27, 2025, 1,938 measles cases have been reported in Ontario in 2025. The majority of those cases (n=1888) were associated with the multi-jurisdictional outbreak that began in Fall of 2024. Most cases are occurring in Southwestern Ontario, with approximately 86% of cases among unimmunized individuals and approximately 7% with unknown immunization status. As of June 3, 2025, there have been two confirmed measles cases in Hamilton residents in 2025. One case was travel related, and one case was linked to the provincial outbreak, acquired outside of Hamilton. Hamilton Public Health Services continues to follow-up with measles contacts and exposures in Hamilton.

As part of the outbreak response, public health units in Southwestern Ontario experiencing increased measles transmission and community exposures are implementing an expanded measles outbreak immunization strategy. These public health units are currently:

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

Hamilton is not currently a jurisdiction recommending an expanded measles outbreak immunization strategy. Hamilton Public Health Services continues to monitor for cases of measles and exposures locally and will continue to provide relevant updates and guidance. Routine immunization is the most effective measure to reduce the risk of measles infection.

Hamilton Public Health Services recommends:

• The routine and high-risk schedule for MMR vaccination.
  • Two doses of measles-containing vaccine are routinely given at 12 months of age using measles, mumps, rubella (MMR) vaccine and at 4 years of age using measles, mumps, rubella, varicella (MMRV) vaccine.
  • Timely administration of routine doses of measles containing vaccine at recommended ages, and catch-up of those who may have missed or delayed vaccination should be prioritized.
  • If the second publicly funded dose is administered earlier than age 4 based on HCP judgement and individual risk, MMR should be preferred for this purpose. 

• For those who live, work, travel, worship or spend time in identified regions that have implemented the expanded outbreak immunization strategy:
  • Infants between 6 and 11 months of age should receive a single dose of the MMR vaccine. Two additional doses of measles containing vaccine are required after the age of one year.
  • Children 1 to 4 years who have received their first dose of MMR vaccine are encouraged to receive a second dose of MMR a minimum of four weeks from the first dose.
  • Adults born after 1970 are recommended to receive a second dose of MMR.
  • Healthcare providers in Hamilton caring for patients who spend time in these affected regions should apply the recommended outbreak vaccine schedule for these patients
  • At this time, if vaccinating on an accelerated schedule, use of MMR should be prioritized (instead of MMRV).
•  Those travelling outside of Canada, particularly to areas where measles is known to be spreading, should ensure they are up to date on measles vaccination.
  • Infants 6 to 11 months of age travelling outside of Canada, are recommended an early dose of MMR vaccine. Two doses are still required after 1 year.
  • Adults born on/after 1970 and all children should be protected with 2 doses of measles-containing vaccine prior to travel outside of Canada.
  • Adults born before 1970 travelling outside of Canada are recommended to receive 1 dose of measles containing vaccine.
  • Please refer to the Publicly Funded Immunization Schedule High Risk Vaccine Program for more information.
•  Health care providers should ensure all staff are immunized with two doses of measles containing vaccine and have immunization records readily accessible for reference in the event of a measles exposure. Laboratory results with proof of measles immunity is an acceptable alternative. 
• 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. They should be vaccinated per the age appropriate catch-up schedule on the Ontario Publicly Funded Vaccination Schedule. 
• Ensure your clinic has appropriate collection kits (NP or throat swabs) on hand that are not expired. Specimens submitted in expired collection kits will be rejected by the lab.
  • To order collection kits, complete Public Health Ontario’s (PHO) Requisition for Specimen Containers and Supplies Form and fax to PHO Laboratory Hamilton at 905-385-0083.
    • Nasopharyngeal swab: virus respiratory kit order #390082
    • Throat swab: virus culture kit order #390081
    • Urine: 90ml sterile container order #390042
• If you have a suspected measles case notify public health immediately, prior to testing. Do not wait for laboratory results. Report all suspect cases to Hamilton Public Health Services:
  • Monday to Friday 8:30 a.m. to 4:30 p.m., call 905-546-2063
  • After hours and weekends, call 905-546-CITY (2489) to speak with the on- call Public Health Nurse.

 If you have any additional questions, please contact the City of Hamilton’s Public Health Services Infectious Disease Program at 905-546-2063.