Do I need a measles vaccine dose? What to know
Respiratory disease is extremely contagious, public health officials say
Measles is a respiratory disease caused by a highly contagious virus that's more infectious than influenza, chickenpox or COVID-19.
Measles illnesses tend to be mild, but the severity can range from ear infections and pneumonia to swelling of the brain called encephalitis — which can lead to convulsions, deafness or intellectual disability. In one case in Ontario in 2024, measles led to the death of a child under age five.
"I'm concerned in that the overall vaccination coverage is much lower in Canada than is needed to stop measles in its tracks," said Dr. Theresa Tam, Canada's chief public health officer.
Measles symptoms include:
- Fever.
- Cough.
- Red, watery eyes.
- Runny nose.
- Koplik spots — small, white spots that occur on the inside of the cheeks.
- A rash that usually begins as flat, red spots on the face and spreads to the trunk, arms and legs.
The virus that causes measles spreads through the air and by contact with respiratory secretions from the nose and mouth.
Droplets containing the measles virus can stay in the air for several hours, and the virus remains infectious on contaminated surfaces for up to two hours.
Here's what public health doctors say about preventing measles.
Why does measles spread so easily?
Contagiousness sets measles apart from other infectious diseases.
A single person "infected by measles can infect nine out of 10 of their unvaccinated close contacts," according to the World Health Organization. "It can be transmitted by an infected person from four days prior to the onset of the rash to four days after the rash erupts."
There's no specific treatment for measles. Doctors work to alleviate symptoms, prevent complications and keep patients comfortable.
Who is at risk of measles?
"All persons who have not had a previous measles infection or who have not had two doses of a measles-containing vaccine are at risk of measles infection," according to the Public Health Agency of Canada's website.
When unprotected infants and children do catch measles, they face a range of possible health impacts.
Among two-year-olds, coverage for one dose of the measles, mumps and rubella (MMR) vaccine decreased from 89.5 per cent in 2019 to 82.5 per cent in 2023, researchers from the Public Health Agency of Canada reported. It also fell among seven-year-olds.
"Vaccination can prevent not only measles infections, but also the really important complications that can arise from measles infection," said Dr. Sarah Wilson, a physician with Public Health Ontario.
The MMR vaccine has been around for decades.
"The main risk [for infection] is vaccination status," said Dr. Ninh Tran, medical officer of health for Southwestern Public Health, which includes Oxford County, Elgin County and St. Thomas in Ontario.
The Canadian Immunization Guide recommends two doses for susceptible groups, such as health-care workers and military personnel.
A dose is also suggested for susceptible travellers born before 1970 who are heading to destinations outside of Canada, according to the National Advisory Committee on Immunization.
Before measles vaccines came on the scene, most people caught the disease. That's why most adults born before 1970 are presumed to have acquired immunity from past exposure.
Vaccination is such an effective tool that measles has been considered eliminated in Canada since 1998, meaning travel-related cases happen occasionally. If local transmission of measles occurs for a year, Canada risks losing elimination status.
People who have had measles once can't get it again, health officials say.
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With files from CBC's Jennifer Yoon