Polio cases in the United States: Canadian doctors call for vaccination

Canadian infectious disease experts are taking notes after US officials reported last week that an unvaccinated American had been diagnosed with the country’s first case of polio in nearly a decade.

Health Canada hasn’t had a case of the virus for more than 25 years, but infectious disease experts say they still have “ears and eyes open to (detect) vaccine-preventable diseases like polio”, which continue to circulate elsewhere in the world.

“Any imported infection is just a flight away,” said Dr. Vinita Dubey, Deputy Medical Officer of Health for Toronto Public Health.

The polio vaccine is part of the standard set of childhood vaccines, but Dr. Dubey pointed out that some parents choose not to vaccinate their children and that the COVID-19 pandemic has delayed vaccination for others.

This creates a renewed risk of vaccine-preventable diseases as people resume international travel after a two-year break, she said. Global polio vaccination efforts were suspended for part of that time, compounding the problem.

A single case of poliomyelitis requires a public health response and must be reported under international health regulations. By the time a case of paralysis due to poliomyelitis is diagnosed, several other people have probably already been infected.

That’s the fear in Rockland County, New York, where a patient was diagnosed with polio after being paralyzed. Officials are holding vaccination clinics and asking health care providers to monitor for possible other cases.

The polio virus is highly contagious and usually causes no or mild symptoms such as mild fever, malaise, nausea, diarrhea, and sore throat. Illnesses are most common in infants and young children, but adults who are not fully immunized can also get sick. The virus attacks the nervous system, with 1-5% of infections causing meningitis and less than 1% leading to paralysis.

Immunisation

Polio cases in Canada declined markedly with the introduction of immunization programs in the 1950s, when up to 5,000 children contracted polio each year. The last case of wild poliovirus in Canada occurred in 1977, while cases associated with oral vaccines were detected until 1995.

Polio infection can result from the spread of a wild virus or from virus transmission after a child has received the oral polio vaccine, which Canada stopped administering in 1996 but is still used. in many other countries.

With the oral vaccine, the virus passes through the body and is excreted in the stool. The virus then spreads easily, infecting the next person when it enters their mouth through hands contaminated with feces. The virus can also live in the throat and spread through respiratory secretions. People who are immune can contract and transmit the virus, but usually do not get sick.

Routine childhood immunization schedules in Canada include injectable polio vaccines before age two and a booster between four and six years of age. The injectable form of the vaccine is inactive and does not transmit the virus from person to person.

Wild poliovirus remains endemic in two countries, Afghanistan and Pakistan, but more than 30 countries reported vaccine-associated polio outbreaks in 2020.

As summer travel is in full swing, experts said adults and children should update their routine vaccinations and check if they need any additional shots for their destination.

“Vaccination hesitancy is another effect of the pandemic,” said Dr. Valérie Lamarre, pediatrician specializing in infectious diseases at Sainte-Justine Hospital in Montreal. It certainly did not improve the situation of vaccine-preventable diseases. »

And while the polio case in the United States is not a threat to Canada, Dr. Lamarre says that doesn’t mean it should be ignored.

“We are going to see these cases appear from time to time. This one simply means “Wake people up. Go get your vaccines,” she said. These diseases are preventable. »

Michelle Ward is a pediatrician, assistant professor and journalist in Ottawa.

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