Why higher measles vaccination coverage matters so much now

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.

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."

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.)