As measles cases continue to rise in Canada, last week brought an uncommon occurrence.
A fully-vaccinated 30-year-old teacher in Ontario contracted the highly contagious infectious disease. This event has drawn the attention of health officials, highlighting its rarity.
The man had close contact with students and teachers at a high school in the York Region, north of Toronto, and the case was likely related to community transmission, the region’s medical health officer said on Monday.
Although fully-vaccinated people can get measles, Dr. Sumontra Chakrabarti, an infectious diseases physician at Trillium Health Partners, stressed how infrequent it is.
“This vaccine is very good at preventing infection, but it’s not 100 per cent. It’s about 95- to 97-per cent effective,” he said.
“So there are going to be people who are fully vaccinated that still might get measles. It still does protect you against the more severe aspects of it.”
This particular case adds to the 17 reported instances of measles across Quebec, Ontario, Saskatchewan, and British Columbia as of Monday. More than half of these cases have been concentrated in the Montreal area.
Measles is one of the most contagious diseases in the world and is airborne. It is so contagious, Chakrabarti said if someone with measles exits a room, others can be infected up to two hours after that person has left.
“The best protection that you have is the vaccination by far,” he stressed. “(The measles) is an exceptionally, if not the most, contagious virus that we know in terms of identified human pathogens. If you don’t want to get infected, you should avoid crowded indoor spaces. But apart from that, it’s something that’s very, very difficult to avoid.”
About the measles vaccine
The measles vaccine is available in Canada as measles-mumps-rubella (MMR) or measles-mumps-rubella-varicella (MMRV) vaccine.
Since its approval in Canada in 1963, the vaccine has led to a decrease of more than 99 per cent in measles cases, according to the federal government.
Number and incidence rates (per 100,000 population) of reported measles cases in Canada by year, 1924 to 2023.
Health Canada
The efficacy of a single dose of the measles vaccine given at 12 or 15 months of age is estimated to be between 85 and 95 per cent. Health Canada states that with a second dose, efficacy is nearly 100 per cent.
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The disease was declared eradicated in Canada in 1988 following an extensive immunization campaign. However, in recent years, it has resurfaced due to a decline in vaccination rates, according to Health Canada. Most cases come from abroad, brought into the country by travellers who are not vaccinated or under-immunized.
The risk of measles spreading is heightened where there are a lot of unvaccinated or non-immune people clustered together in regions or communities. And while measles vaccination rates are high in Canada, Health Canada said they are still below “the necessary threshold for community immunity in some places.”
The target vaccination coverage for measles is 95 per cent, according to Health Canada.
The 2021 Childhood National Immunization Coverage Survey shows that 91.6 per cent of two-year-olds in Canada have received at least one dose of a vaccine.
“The target vaccination for measles in the community would be 100 per cent, that would be my dream,” Chakrabarti said. “But when you start to get anywhere above 95 per cent to 97-per cent coverage, that’s when you have an excellent wall of protection.”
Who should get the measles vaccine?
The measles vaccine is recommended for anyone over the age of one. The vaccine is administered as a two-shot series, with the first shot given at around 12 to 15 months of age. The second shot is given at 18 months or between ages five and six years (before your child starts school), according to the Canadian Pediatric Society.
Infants under the age of one could potentially receive the measles vaccine and Chakrabarti recommended parents consult with their health-care provider for guidance.
Although the measles vaccine was initially available in the 1960s, in 1971, it was combined with the mumps and rubella vaccines to create the three-in-one MMR shot.
Adults born before 1970 can be “presumed to have acquired natural immunity to measles,” according to Health Canada, and only one dose is recommended.
“Before the 1970s, most people would have been infected with measles, and so that infection provides them with a level of immunity,” explained Matthew Miller, the director of the Degroote Institute for Infectious Disease Research at McMaster University.
“That is why they really need one dose of the vaccine to boost that immunity and give them really strong additional protection,” he said.
For adults born after the 1970s, two doses are recommended.
Chakrabarti said if you are unsure how many measles shots you received, there are a few ways to find out.
The first option is to visit your family physician, who may already have your vaccination record on file. If your record isn’t available, Chakrabarti reassured that there’s no harm in receiving an additional dose.
“If you already had two doses and you get a third one, it’s not going to be harmful. But if you’ve only gotten one dose, it certainly can help,” he said.
Health-care providers also offer blood tests to verify vaccination status, he added.
What happens if you get the measles?
Miller and Chakrabarti underscored that vaccination remains the most effective defence against measles.
If you’re vaccinated and contract measles, the symptoms are typically milder.
“The reasons that happen sometimes has to do more with an individual’s health status than with how good the vaccine is,” Miller said. “There are people who may have sort of undetected immunological deficiencies at the time that they become vaccinated. And so that vaccine just doesn’t work as well in those types of individuals, which can lead them more susceptible to infection.”
However, Miller cautions that without immunization, you face a higher risk of severe complications and spreading the disease to others.
“One of the things that people don’t recognize, because most people would not have experienced measles in the recent past, is how severe measles can be for children who do become infected. It’s not something to be trivialized,” Miller said.
When you become infected with the measles virus, you may experience a range of symptoms. Initially, you might have a high fever, cough, runny nose, and red, watery eyes. After a few days, a characteristic rash typically develops, starting on the face and spreading to the rest of the body.
But measles can also lead to severe consequences, especially in children.
This includes cases of “bad viral pneumonia, brain inflammation, deafness, and a very scary thing called SSP, where a young child can get measles and completely recover from it,” Chakrabarti explained. “But then in the next 10, 15 years, they all of a sudden get a decline in their cognitive function to the point that they’re in a vegetative state.”
He added that while measles cases are on the rise in Canada, this trend has occurred in the past, so it’s not unprecedented. He emphasized that vaccines have proven highly effective in halting the spread of measles previously.
— with files from the Canadian Press