When measles rears its head, young, unvaccinated children bear the brunt of the disease | CBC News

· Posted: May 18, 2024 4:00 AM EDT | Last Updated: May 18

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An Ontario child's death from measles this year offers a grim reminder: When vaccination rates drop and this virus rears its head, the youngest among us bear the brunt.

Public Health Ontario (PHO) reported the recent death of a child under five on Thursday. The child, from Hamilton, was one of five unvaccinated kids who fell ill and ended up in hospital this year, with 22 cases of measles in total reported so far across the province.

That means, in mere months in 2024, Ontario has hit nearly a quarter of the roughly 100 measles cases documented in the entire decade beforehand. And PHO said this year's death marks the province's first deadly case since 1989 — as far back as its data goes.

Renowned infectious diseases specialist Dr. Allison McGeer called it a tragedy, but not a surprise.

"It's something that people have spent a lot of time and effort to try to avoid," added McGeer, who works at Sinai Health System in Toronto. "There's also a certain aspect of inevitability to it just because of how much ground we lost in measles vaccination around the world."

Globally, and in Canada, immunization rates against various infectious diseases have backslid in recent years. That's given measles — once thought of as a disease of the past — a chance to come roaring back. 

In Ontario, for instance, the proportion of seven-year-olds who had zero vaccine doses rose dramatically, from less than four to nearly 17 per cent, between the 2019-2020 season and 2022-2023, a March PHO report noted.

"Many people might have missed a dose of a vaccine during the darker days of the pandemic when several public health programs were curtailed because of the enormous impact that COVID was having," said Dr. Isaac Bogoch, an infectious diseases specialist with the University Health Network.

It's a similar scene elsewhere. Measles cases spiked this year in Montreal and other parts of Quebec; infections in the U.S. have already hit their highest level since 2019; and outbreaks keep appearing globally, including an ongoing cluster of cases in London.

People travelling to and from hot spots also means this virus is now routinely hopping around the globe, as PHO noted in its latest report, with 15 of the province's recent cases directly tied to travel abroad.

It's also highly contagious: Measles can linger in the air for hours, and one infected person can spread it to nine out of 10 unprotected people around them. 

Most at risk? Children who aren't yet vaccinated, multiple medical experts stressed.

Vaccines remain highly effective

"If you look at the data from any of the provinces," McGeer said, "it's unvaccinated kids who are the problem."

That's because measles is a one-and-done infection. If you catch the virus once, you're protected against a serious infection for life — meaning most older adults have immunity, either through prior exposure, vaccination or both.

Babies and young children, on the other hand, are often quite vulnerable, particularly if they're simply too young for their first vaccine dose.

"If a mother has immunity to measles, that immunity is transferred to the baby," noted Dr. Donald Vinh, an infectious diseases specialist with McGill University in Montreal. "But it's not forever."

Canadian kids typically get their first round of the two-dose combined measles, mumps and rubella vaccine at 12 to 15 months old, so there's a window of time when infants may be unprotected.  

But just one shot is thought to have an efficacy level of upwards of 85 per cent, federal figures suggest, while the full set of doses has an efficacy level of nearly 100 per cent. Many experts also recommend that infants travelling outside the country can get an extra dose earlier than 12 months old, leading to a three-dose series in those cases.

When overall vaccination rates drop, unvaccinated kids can easily catch this highly contagious virus, stressed pediatrician Dr. Caroline Quach-Thanh, a professor at the University of Montreal.

In some cases, that could be the result of parents choosing to avoid immunization for their children. But Quach-Thanh noted that immunocompromised kids, including those having chemotherapy, simply can't get the measles vaccine as it contains a weakened form of the virus — a type of shot that's highly effective in the general population but risky for people with compromised immune systems.

"And so if we vaccinate them, it might lead to measles because their immune system is just too weak to control the vaccine," Quach-Thanh explained. 

WATCH | How to protect yourself from measles: 

How to protect yourself against measles

Dire health impacts for unvaccinated children

When unprotected infants and children do catch measles, the illness is often mild. But there's also a wide range of possible health impacts besides its telltale rash. 

Measles is thought to be deadly in one in every 3,000 cases, Quach-Thanh said. It's also known for causing other life-altering ailments like pneumonia, brain inflammation and hearing loss. 

She also pointed to research suggesting devastating health issues can crop up years after an initial infection, including a condition known as subacute sclerosing panencephalitis (SSPE), or Dawson disease. The progressive neurological disorder is persistent, disabling and eventually leads to death.

One study from researchers in California, published in the medical journal Clinical Infectious Diseases in 2017, showed a high rate of Dawson disease cases among unvaccinated children, particularly those infected with measles during infancy.

"SSPE demonstrates the high human cost of 'natural' measles immunity," the research team wrote.

WATCH | How Quebec battled this year's measles outbreak: 

How Quebec has held off a major measles outbreak so far

Quebec efforts to curb measles cases

Curbing those kinds of health impacts requires higher immunization levels, experts agree. And this year, Quebec proved progress is possible.

Despite having pockets of school vaccination rates as low as roughly 30 per cent, the province managed to curtail its spike in infections through contact tracing efforts, post-exposure vaccination for high-risk contacts and what Quach-Thanh called "aggressive" efforts to raise school vaccination rates.

The strategy seemed to work: Cases largely stabilized, with a current total of 51 infections so far this year, including nearly half of those in Montreal.

And, thankfully, no deaths.

"We've been lucky," Quach-Thanh said. "It could have happened to us."

ABOUT THE AUTHOR

Lauren Pelley covers health and medical science for CBC News, including the global spread of infectious diseases, Canadian health policy, pandemic preparedness, and the crucial intersection between human health and climate change. Two-time RNAO Media Award winner for in-depth health reporting in 2020 and 2022. Contact her at: lauren.pelley@cbc.ca

• @LaurenPelley

With files from CBC Health, CBC Toronto