How fading dread of deadly diseases could let them stage a comeback

It’s a cruel paradox: When diseases disappear thanks to public-health interventions people forget how awful the diseases were and become indifferent or hostile to the intervention, making it more likely the deadly diseases return, researchers warn.

In other words, vaccines are a victim of their own success, as diseases they’ve conquered make a comeback. We may have forgotten whooping cough or polio, and the enormous effort needed to keep them under control. But they haven’t forgotten us.

Measles killed over two dozen Toronto children in 1890, decades before a vaccine was developed.

Until the mid-1950s, measles killed as many as 75 people a year in Canada and caused hundreds of cases of encephalitis, a swelling of the brain that can causes lifelong damage. The 1960s changed all that: Vaccines made measles a disease of the past – for the most part. Ontario had tens of thousands of measles cases a year in the early 1960s, but a relative handful by the 1980s.

Many diseases that are now vaccine-preventable often permanently damaged the children they didn’t kill, said Toronto-based medical historian Christopher Rutty.

“Pertussis is very debilitating. It’s deadly to the very, very young, those too young to get vaccinated, because they can’t handle non-stop coughing – it leads to brain damage due to the lack of oxygen.”

Diptheria, an upper respiratory tract infection which was incurable before an antitoxin was developed in the 1890s, terrified families and reduced doctors to miserable helplessness.

“I recall the case of a beautiful girl of five of six years, the fourth child of a farmer’s family to become the victim of diphtheria,” a doctor remembered in 1928.

“She literally choked to death, remaining conscious until the last moment of life.”

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“I felt, as did every physician of the day, as if my hands were literally tied, and I watched the death of that beautiful child feeling absolutely helpless to be of any assistance.”

“That kind of story was pretty common, to watch a kid basically strangle,” Rutty said.

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But as the memory of what infectious diseases, now leashed by vaccination, are like to endure is fading. And so is fear of them, and motivation to protect children from them.

“It’s easy, in some ways, to blame people, to say ‘Why aren’t you getting the vaccine?’” Rutty said. “But at the same time there’s a cohort of people who have grown up in the last couple of generations that have never seen polio, or have never seen diphtheria, and how are they really supposed to know? ”

Widespread vaccination brought diphtheria under control in Canada starting in the mid-1920s. In Hamilton, Ont. where in a bad year diphtheria could kill dozens of people, vaccination virtually eliminated the disease after 1925. Before that date, it had been the leading cause of death of Canadian children.

“Diphtheria could come back easily,” Rutty said.

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After the fall of the Soviet Union in the 1980s, the collapse of Soviet-era vaccination systems led to a diphtheria outbreak.

Portrait of a vaccine-free Toronto

In 1891, more than 1,700 people under the age of 15 died in Toronto, 1,207 of them under the age of one – more than a quarter of all the babies born that year.

That’s probably an underestimate: some deaths attributed to pneumonia would have been due to measles or influenza; also, many infant deaths are very informally accounted for by modern standards.

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GRAPHIC: JANET CORDAHI

Vaccination follows a predictable cycle, says University of Toronto epidemiologist David Fisman.

First, a disease afflicts and terrifies a society. Then, doctors develop a vaccine. The society, with fresh memories of the disease, embraces the vaccine.

“In the 1950s, people were so desperately frightened of polio that, notwithstanding the fact that they had real vaccine-related disasters, parents still lined up to get their kids vaccinated,” he explains. “They still wanted the vaccine, because they were much more frightened of the polio than the vaccine.”

The vaccine’s success leads to complacency: The disease is just held at bay, not defeated, but that effort isn’t visible.

“After a while, memory fades as to what measles was. And people just assume that that’s the way the world is,” Fisman said. “They don’t realize that that‘s a tangible output that requires ongoing effort to maintain, and that if you don’t have that ongoing investment it goes away.”

With fewer people willing to vaccinate, the disease returns – perhaps quickly. “Explosive increases in disease risk can occur very suddenly with only small declines in vaccine coverage in the population,” reads a 2013 Toronto Public Health report that Fisman co-authored.

The report predicts the return of measles, pertussis and polio after a fall in vaccine coverage.

“I’m quite worried about polio,” Fisman said. “Polio is sort of a silent thing, where most people are just going to get a run-of-the mill gastrointestinal disease.”

“You don’t know that polio is back until you start seeing flaccid paralysis in children, and that is going to be a high price to pay.”

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“The mechanics of what happens when you have these changes are pretty predictable. If I throw a ball into the air, it’s going to come back to earth,” Fisman said.

“If I stop vaccinating against polio in a world where there’s lots of polio transmission in countries that have close connections to Canada, and I lose my immune herd in Canada, of course we’ll see polio cases in Canada, and we’re likely to see them in big urban centres. There’s not a lot of guesswork.”

“If we don’t vaccinate, this stuff comes back.”

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