Why higher measles vaccination coverage matters so much now

CBC

21-03-2025

Measles is so infectious that when under-vaccinated individuals mingle, they'll always be at risk. That's why public health officials are stressing the importance of high vaccination rates amid backsliding and growing outbreaks.
The disease is spreading across the country, with hundreds of cases reported this year and the majority in Ontario. The resurgence comes amid falling childhood immunization rates; measles was declared officially eradicated in Canada in 1998, aside from the occasional travel-related case.
The virus spreads easily through airborne droplets and usually causes fever, cough and redness of the eyes to start. What follows includes white spots next to the molars and a distinctive red rash that usually starts around the hairline and moves down the body.
Before effective measles vaccines were developed, most children got the disease and eventually recovered. But physicians stress that it can cause severe complications and can result in hospitalization, including intensive care. In Canada, 12 per cent of cases this year required hospitalization, according to data compiled by the federal government.
"What's devastating is that this is preventable" with vaccination, said Dr. Caroline Quach, a pediatric infectious diseases specialist and medical microbiologist at Ste-Justine Hospital in Montreal.
Complications can include pneumonia, death
Raising measles vaccination coverage in pockets of communities with low rates really matters now because when the spark of an infection is introduced, it spreads like wildfire among people of all ages who are susceptible.
The measles, mumps and rubella vaccine comes in two doses; one is done before two years of age and the other by seven. Coverage for the first dose decreased from about 90 per cent in 2019 to around 83 per cent in 2023, according to the Public Health Agency of Canada. For the second dose, it fell from about 86 per cent to around 76 per cent over the same time period.
Complications of measles infection include pneumonia, encephalitis — the inflammation of the brain — and even death, Quach said.
It can also lead to lifelong deafness and blindness, and a rare but fatal brain disorder called subacute sclerosing panencephalitis can develop years later.
"People don't realize that these consequences still happen and that we still don't have a treatment for measles," Quach said.
Those born before 1970 and who were raised in Canada are considered protected against measles because it was so rampant. Over time, those individuals represent less of the overall population, Quach said.
"We really have now to rely on very high vaccination coverage if we want to limit the spread of measles."
A matter of when, not if, measles returns
Those at the highest risk of severe disease from measles include vulnerable populations — like infants who are too young to be vaccinated, pregnant women, and anyone with a weakened immune system, said Dr. Tina Tan, a pediatrics professor at Northwestern University's Feinberg School of Medicine in Chicago.
In places facing measles outbreaks such as Ontario, Texas and New Mexico, public health officials are offering vaccination to immediately protect infants as young as six months. (These babies will still need two full regular doses for longer-term immunization.)
"When vaccination rates drop in a community, it is not a question of if, it's a question of when measles is going to come because it is so incredibly contagious," Dr. David Higgins, a pediatrician at the University of Colorado, told reporters in a virtual briefing.
Higgins said "huge" disruptions in routine childhood vaccination campaigns in places like the U.S. and parts of Europe, Africa and Southeast Asia during the COVID-19 pandemic mean the disease is just a plane flight away.
Outbreaks occur in local communities where people are susceptible to infection because of low immunization rates, Higgins said. National vaccination coverage levels may not reflect the local situation.
Looking at southwestern Ontario
Case in point? Southwestern Ontario's outbreak.
Many of the cases in Canada were sparked by an international traveller who attended a wedding in New Brunswick in October 2024. In Ontario, as of Thursday, all but seven of the province's hundreds of cases this year were linked to that outbreak.
More than 30 people in Ontario, largely in the province's southwest, with measles have needed hospitalization, including two in intensive care. Most of those hospitalized have been unvaccinated children, said Dr. Christine Navarro, a public health physician with Public Health Ontario.
In a report this week, the agency attributed the rise in cases to transmission among unvaccinated people.
In Canada, immunization rates for two doses of the vaccine given before school entry also declined during the pandemic, contributing to backsliding, doctors say.
Repeated surveys suggest the vast majority of parents in Canada want their child to be immunized against preventable infectious diseases including measles, while about three to five per cent are outright against all routine childhood vaccinations, Quach said.
Families as vaccination partners
Provincial catch-up campaigns aim to have 95 per cent of the population vaccinated to prevent person-to-person spread of measles among those who are susceptible.
In Ontario, just 70 per cent of seven-year-olds were considered fully vaccinated against measles during the 2023-24 school year, said Navarro. Reasons include reduced reporting and missed doses, she said.
WATCH | This is the way measles attacks:
Measles: Understanding the most contagious preventable disease | About That
1 year ago
Duration 10:16
There are early signals that measles — one of the world's most contagious but preventable diseases — may be spreading in parts of Canada. Andrew Chang breaks down the way the virus attacks the body and what makes it so contagious.
"People who are vaccinated are much less likely to become cases, and if they do happen to become infected, they're much less likely to continue to transmit that disease," she said.
Quach, the Montreal pediatrician, said Quebec has a program for every family who gives birth to encounter doctors, nurses or pharmacists who discuss routine vaccinations with them and answer questions, without being judgmental.
One effective method is having both top health officials and trusted community members on the ground to present the facts to questioning or hesitant people, Higgins said.
"We need to approach them as partners," he said. "We are trying to work together to help their communities, to help their families and their children thrive."
In southwestern Ontario, the focus remains boosting vaccination coverage.
Grand Erie Public Health's unit has 112 cases of measles, said Dr. Adelle Chang On, its acting medical officer of health, on Friday. (The unit serves Brantford and surrounding Brant, Haldimand County and Norfolk County.)
It won't be able to declare the outbreak over until at least two incubation periods, or 42 days, of the last reported case.
Even then, Chang On said, her team will stay vigilant, given potential sparks could reignite chains of transmission as people travel.