Q&A: Comparing COVID-19, polio and the vaccines

The polio vaccine was introduced in 1955, and by 2022 it has all but been eliminated worldwide.

However, COVID-19 vaccinesaren'tlikely to take the same route.

Stefani Langenegger, host of CBC'sThe Morning Edition,asked Dr. Angela Rasmussen, a virologist and researcher with the University of Saskatchewan's vaccine and infectious disease organization, to chart the difference.

The conversation has been edited for clarity and length.

Langenegger:How did the polio vaccine work so effectively?

Rasmussen: Polio itself is a very different disease than COVID-19, so it's helpful to understand how the two types of vaccines actually work for polio.

Polio is a gastrointestinal disease, actually.You get it through the oral route by ingesting it. And then in some caseswhen it causes poliomyelitis, which is the disease that it causes, it actually gets out of your gut and gets into your central nervous system. and that's how it causes paralysis.

There's the oral polio vaccine that is a live attenuated vaccine [a version of the living virus that has been weakened so that it does not cause serious disease in people with healthy immune systems]. So it's a polio virus that is actually not virulent that you take orally, and one dose of that provides lifetime immunity.

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And then there's the Salk vaccine that prevents the virus from leaving your gastrointestinal tract and getting into your neurons, thereby causing paralysis.

So it doesn't prevent infection, it prevents the virus from actually causing disease. And that's one of the reasons why, even after the vaccines were introduced, the incidence of polio disease went way down very quickly.

But polio virus itself actually was around for decades longer and it's still around in some countries today where there's not enough vaccination.

How does it compare with COVID-19?

It took many, many years with very, very high global vaccination rates to actually eliminate some of the polio virus flavours that are out there and it really is going to require very, very high levels of immunity and that's not the place that we are at right now with COVID-19.

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There's still billions of people worldwide who haven't been vaccinated yet. So if we're expecting the COVID-19 vaccines to do the same thing as polio, we're still going to need to vaccinate a whole lot of people.

Are the vaccines for COVID-19 doing their job then in that disease seems to be reduced for those of us who are fully vaccinated?

They are, and in that waythe COVID 19 vaccines are working similarly to the polio vaccine.

But polio virus and SARS-CoV-2 are very different viruses that cause disease in very different organ systems.

The vaccines that are out now do protect against severe disease for most of the people that have them.

Now, polio virus doesn't have as many evolutionary possibilities as SARS-CoV-2.

From your immune system's perspective, there's really only three flavours of polio. From your immune system's perspective with SARS-2, on the other hand, there are many different flavours because the virus keeps transmitting, it keeps mutating, we keep seeing new variants in part because there are large populations of unvaccinated people.

So the virus in that way is a lot trickier for the immune system to keep up with than polio was, and that's why you still see people who are immunized against SARS-CoV-2 still getting breakthrough infections, especially with variants that are very different, like Omicron.

What might that mean for a fourth dose?

So it's really not uncommon for vaccine regimens to have multiple doses, and it's entirely possible that we may need a fourth dose. As you know, in the U.S. this past week, they've approved fourth doses for people over the age of 50.

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I think that there is data from Israel primarily that suggests that that is a good idea for people who are at high risk, because that fourth dose really does continue to cut the incidence of mortality of people who are infected.

Will everybody need a fourth dose? That's really hard to say. I think that there's not a lot of evidence that shows that people who are not at high risk really need that fourth dose that it provides significant benefit beyond the third dose.

I think it's also totally possible that as we see new variants continue to emerge and they will as long as there are a lot of unvaccinated people in the worldthat we may need a fourth dose of a variant-specific booster shot.

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