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Measles - UPDATED March 27, 2024

On March 26, 2024, the Simcoe Muskoka District Health Unit was notified by Public Health Ontario’s (PHO) laboratory that due to laboratory error, the measles case the lab had confirmed as a positive result on March 12, 2024, is in fact negative for the measles virus. With this new information we believe that that individual was not infected with measles and that there has not been exposure to measles resulting from this individual’s illness.

We are aware that public notification of the case on March 12 may have created worry, anxiety and disruption for some, and we acknowledge and regret this. Unfortunately, we do know that, despite best efforts, on rare occasions lab errors can occur. We are working closely with PHO’s laboratory to do all that we can to ensure that such an incident does not occur again.

Although we are relieved that this case has now been lab-confirmed as negative, measles is still active in Ontario at this time and the potential remains for new cases to arise, especially given the increase in Ontarians travelling to areas in the world that have higher numbers of measles cases. Measles is a very contagious airborne virus that spreads easily from an infected person when they breathe, talk, cough or sneeze. Measles virus can live up to two hours in the air after an infected person leaves the area. It can quickly spread among people who are unvaccinated.  Vaccination offers excellent protection against measles, and we advise individuals to keep up to date with their routine immunizations, including measles, mumps and rubella (MMR) vaccination. 

Symptoms of measles can begin anywhere from 7 to 21 days after being exposed to the measles virus and include:

  • fever,
  • cough,
  • runny nose,
  • red eyes,
  • feeling tired,
  • small white spots in the mouth and throat (not always present),
  • red blotchy rash that starts on the face and spreads down the body and lasts at least three days.

Infants under 12 months and people who are pregnant or have a weak immune system can get very sick from measles.

Measles can also lead to complications including middle ear infections, pneumonia, diarrhea, or encephalitis (swelling of the brain) and occasionally death in the very young. Measles in pregnancy can lead to premature delivery, low birth weight and miscarriage.
  • Isolate immediately by staying home and avoiding contact with others.
  • Contact your health care provider if you think you may have measles. Your health care provider will assess you for measles and will test you if they suspect you have measles.
  • Call before visiting a clinic or hospital so they can prepare for your arrival and prevent the virus from spreading.
  • Wear a well-fitted mask when seeking medical assessment.

The measles virus is in the nose and throat of an infected person. It can spread easily to others when they come in contact with droplets of an infected person or the air when an infected person has breathed, coughed or sneezed. The virus can enter the body through the eyes, nose, or mouth.

Someone who is contagious with measles can spread it to others from four days before a rash appears to four days after the rash appears.

Measles virus can live up to two hours in the air after an infected person leaves the area.

At this time the most important measure you can take is to ensure your vaccinations are up to date.


Check vaccination status for you and your family members to make sure you have two doses of measles vaccine (M, MR, MMR, MMRV).

  • Born before 1970? You likely had the measles virus as a child and are protected if you did but can get vaccinated if you are unsure.
  • Born between 1970 – 1996? Double check you have two doses of a measles vaccine (A two-dose series was not introduced in Canada until 1996 so you may not have the recommended two doses).


Please follow up with your health care provider if you would like more information or to arrange an appointment. If you do not have a health care provider or are unable to see them, please book an appointment at one of our health unit offices.

Ontario’s Chief Medical Officer of Health and the health unit recommend that people who are not up to date with their measles immunization receive a dose of the measles (MMR) vaccine including:

  • Infants aged six to 11 months of age who will be travelling to areas with increased measles transmission.
  • Children aged four to six years of age.
  • Children who missed their second dose of MMR vaccine.
  • Adults aged 18 years and older who have previously received one dose of MMR vaccine should receive a second dose if they are health care workers, military personnel, post-secondary students, planning to travel outside of Canada or based on the health care provider’s recommendation.

For more information on measles vaccine recommendations visit our Immunization Clinics page.

Page last updated March 27, 2024

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