Friday, March 31

Polio is back on the radar of Canada and other countries. Here’s why

Polio, an infectious disease that was eradicated in Canada nearly three decades ago, has re-emerged in some Western nations despite widely available and effective vaccines against the illness.

And although Canadians are largely vaccinated against the disease that can cause paralysis or death, the disruptions from the COVID-19 pandemic that have led to children missing routine immunizations, or vaccine hesitancy fueled by pandemic misinformation, could leave some vulnerable to an illness that was long thought to be in our rear-view mirror, experts say.

On Thursday, the Public Health Agency of Canada announced it plans to test wastewater across the country for traces of the polio virus.

Other countries, meanwhile, have started vaccination campaigns to deal with new cases.

In London, England, children age one to nine became eligible for a polio booster shot Wednesday as British health officials say they’ve found evidence that the virus has spread to multiple parts of the city. Testing sewage water from eight boroughs in London has led officials to believe that transmission has spread beyond “a close network of a few individuals,” said Britain’s Health Security Agency. The polio vaccine is already a part of routine immunizations for British children.

And in the United States, the country last month reported its first case of polio in 10 years.

The Star spoke to infectious disease experts about polio and whether Canada should be prepared for an outbreak of its own.

Here’s what they said.

First off, what is polio and what are its symptoms?

Polio, short for poliomyelitis, is a serious illness in which a virus attacks a person’s nerve cells in the spinal cord. It can leave muscles weak or damaged, and, in very serious cases, it can permanently damage nerves that control the muscles and leave a person paralyzed (although less than one per cent of cases lead to irreversible paralysis).

Death can occur when the paralysis affects the muscles that help control breathing.

Other symptoms can include sore throat, fever and exhaustion.

The first case of polio in Canada was reported in 1910. Waves continued for the next few decades and peaked in 1953, when there were more than 9,000 cases of polio and close to 500 deaths reported.

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Polio is “very contagious” and spread through the fecal matter of an infected person. It can also be spread through coughs or sneezes, according to Ontario Health.

Ninety per cent of people who have the illness do not show any symptoms. Children in Canada receive vaccines for polio four times during infancy, at two, four and six months and then again at 18 months, according to PHAC.

How was it largely eradicated in Canada?

Parents and children wait outside the Riverside Public School in Elmira, NY, on July 1, 1953, to get the polio vaccine.

In Canada, the last polio cases were reported in 1994, according to Ontario Health. Vaccination campaigns through Canada and many other nations from the 1950s to the 1990s caused polio to largely disappear from populations.

“However, it was never fully eradicated in countries like Afghanistan and Pakistan, and periodically there are parts of the world where if there was a disruption of their vaccine campaign, like a war, there might be local outbreaks,” said Dawn Bowdish, a professor of pathology and molecular medicine at McMaster University.

Canadians are fortunately mostly vaccinated against polio, said Bowdish.

A strong vaccination program in Canada, in which Ontario and many other jurisdictions require children to be up to date on polio vaccinations to attend school, is one of the main reasons for the success in beating back the illness, said Dr. Sameer Elsayed, a professor of infectious diseases and microbiology at Western University.

According to 2020 numbers from the Public Health Agency of Canada, about 90 per cent of children in this country were considered vaccinated for polio.

“We’ve been able to keep polio at bay; there haven’t been cases, and, so far in Canada, there hasn’t been evidence of polio in wastewater, like the UK,” Elsayed said

Where has it come back—why?

Medical researcher Dr. Jonas Salk studying slides in his laboratory, following the invention of his pioneering polio vaccine, circa 1957.

Officials in London, England, have found polio virus samples in wastewater, and a case of polio was found in New York state in late July.

Jerusalem had an outbreak of several polio cases in the spring, the first in more than three decades.

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Bowdish said the re-emergence of polio in Western nations could be due to imported cases, if an unvaccinated person traveled to a part of the world where the virus has not been eradicated.

“It’s not totally unexpected to occasionally find this in the wastewater, but where it’s increasingly concerning now is because of the COVID pandemic and public resistance to vaccination … there are going to be some people who are unprotected,” she said.

In parts of the Global South where polio has not been eradicated, it’s largely due to unequal access to vaccines or the fact that poorer nations have had to rely on a version of the vaccine that is considered outdated in the West and taken orally that contains a live version of the virus, said Elsayed.

The oral vaccine was developed in the early 1960s and was widely used in the US until 2000. Canada also used this vaccine for “many years” and switched to the current inactivated poliomyelitis vaccine, that does not contain live virus, in 1995, according to the federal government.

The switch was made as the oral vaccine was associated with cases of paralytic polio from 1980 to 1995 in Canada.

While the oral vaccine is effective, much of the western world has switched to the more expensive inactivated vaccine, though the oral vaccine continues to be used globally, particularly in the Global South.

If the oral vaccine is given to an immunocompromised person, it can replicate within them and now what was a weakened form of the virus can transform into a version that causes illness, the CDC explains on its website. The person who has that transformed virus in them could infect someone else who is unvaccinated through their fecal matter, typically happens in environments with poor sanitation.

The case of polio identified in the US was caused by “vaccine-derived poliovirus type 2” in an unvaccinated individual, the Center for Disease Control and Prevention states on its website.

“These vaccine-derived strains of polio are found in the environment, in water systems. Theoretically, they can circulate and cause transmission for people who have not been vaccinated,” said Elsayed.

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If the vaccines used in the West that do not contain the live virus were distributed more equally in the world, countries would not have to rely on the oral vaccine and cases related to the oral vaccine would be non-existent, he said.

Is there any connection to the pandemic?

This illustration made available by the US Centers for Disease Control and Prevention depicts a polio virus particle.

Increased vaccine hesitancy around the pandemic and delays in getting children vaccinated against multiple illnesses due to pandemic shutdowns can leave the population more vulnerable, said Bowdish. But the fact that the majority of the population is inoculated means most have strong protection against a virus like polio, she said.

Colin Furness, an infection control epidemiologist at the University of Toronto, said that the anti-vaccination movement has been “energized” by the COVID-19 pandemic, which is a concern, especially when it comes to illnesses such as polio.

“The injectable vaccine we have now does not have live virus and it’s incredibly effective, but there are more people refusing vaccination,” he said.

How worried should I be?

A Pakistani health worker administers polio vaccine drops to a child during a vaccination campaign in Karachi on December 10, 2018.

When it comes to infectious diseases to be concerned about, Furness said he’s more worried about COVID-19 and monkeypox. The Canadian population remains highly vaccinated against polio, he said.

What Canada needs to do is focus on getting everyone up-to-date on routine vaccinations, said Bowdish.

“We want to make sure we really focus on the very young and anyone who’s been missed for any reason,” she said.

With files from The Associated Press


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