Having COVID-19 again and again

For the second time this year, Justin Trudeau announced this week that he has tested positive for COVID-19. The Prime Minister is the embodiment of a reality that awaits us all: we can be reinfected by SARS-COV-2, the virus that causes COVID-19. And of course we will be.

Posted at 1:00 p.m

Catherine Handfeld

Catherine Handfeld
The press

“If we draw parallels with other viruses, for example influenza, we risk having multiple SARS-COV-2 infections over our lifetime,” says Jesse Papenburg, a pediatric infectious disease specialist, microbiologist and epidemiologist at Montreal Children’s Hospital.

Why can we get infected again? Mainly for three reasons, according to Dright Papenburg.

First, some people have not developed adequate immunity to the initial infection, either because they are immunocompromised or simply through bad luck; then the level of antibodies decreases over the months (protection is better in the first three to six months); After all, viruses evolve over time.


The Dright Jesse Papenburg, pediatric infectious disease specialist, microbiologist and epidemiologist at Montreal Children’s Hospital

Since March 2020, SARS-COV-2 has been arriving in successive waves, constantly threatening the population with a new variant. However, experts expect that the epidemiology will change and risk periods will become less frequent in the future.

“Theoretically, someone can be affected in every wave if the variant changes significantly,” says Dr.right Bruce Mazer, Associate Scientific Director Strategy for the COVID-19 Immunity Task Force and Professor of Pediatrics at McGill University. “But I think a frequency of infection every two or three years would be more in line with our expectations for an endemic virus. »

some protection

It is unclear exactly how SARS-COV-2 will be assessed or how the immune system will respond over the long term. But according to epidemiologist Jesse Papenburg, the example of the H3N2 flu may give us some clues as to what to expect.

The H3N2 virus caused a pandemic in 1968 that caused more than 1 million deaths. Fifty years later, it’s still one of the sources of influenza, which is responsible for seasonal epidemics that hit vulnerable people harder but cause far fewer deaths than in 1968. Why? Because the population has developed sufficient immunity.

With COVID-19, we realize that even if the risk of reinfection increases over time, we still have some protection against hospitalization and serious infection.

The Dright Jesse Papenburg, pediatric infectious disease specialist, microbiologist and epidemiologist at Montreal Children’s Hospital

This is the memory response: the immune cells remember the pathogen, initially thanks to vaccination, but also thanks to infections with similar variants.


Benoit Barbeau, Virologist, Professor in the Department of Life Sciences at UQAM

“Yes, you have a good chance of being infected again, but that does not mean that you will have more serious symptoms, on the contrary,” summarizes virologist Benoit Barbeau, professor in the Department of Life Sciences at UQAM.

Studies suggest that hybrid immunity – combining a first series of vaccinations and infection – seems to offer the best protection.

No guarantee

According to the latest data, 40% of Canadian adults have contracted the Omicron variant. Because the population was largely vaccinated and Omicron is less virulent, the vast majority of those infected survived without severe or persistent symptoms.

If you are part of this happy majority, you may have the pleasant impression that you will never suffer from a more serious COVID-19. “I would like to say that it will be, but it will really depend on the mutations,” replies the Dright McGill’s Bruce Mazer.

The omicron variant suggests that we are in a general trend where the virus is becoming less and less pathogenic, “but nothing is certain,” recalls virologist Benoit Barbeau, who also draws a parallel with influenza, some of which Seasons are heavier than others.

At the population level, the Dright Jesse Papenburg believes we are heading towards less and less severe COVID-19 infections, “but on an individual level, a mild COVID experience is no guarantee that the next COVID infection will be as mild.” Even in vaccinated individuals who already had an infection, there is still a risk of serious illness.

Next fall, if we should see an increase in cases, vaccines better suited to the variants that are in circulation should also be offered. Don’t hesitate to take advantage of it, believes the Dright macerator “During this omicron wave, mortality is much lower than before, and vaccination has played a very important role,” he says.

COVID long

According to UK data published this spring and based on the Omicron variant, vaccinated people have an 8% risk of contracting COVID for at least a month. Does this mean we take that risk every time we contract COVID-19? The course of the percentage risk of having long COVID is unknown, but it is possible that it decreases from one infection to another, estimates virologist Benoit Barbeau.

Cumulative effect?

In the most severe cases of long-lasting COVID, the SARS-COV-2 virus can damage the heart, lungs, brain and blood vessels. Can consecutive infections have a cumulative effect? Again, there is no indication that this will be the case. According to Dright Bruce Mazer, associate scientific director of strategy for the COVID-19 Immunity Task Force and professor of pediatrics at McGill University, said the effect could be cumulative in frail people who didn’t have time to heal between the two infections. “You see that with all infections, not just COVID-19,” he says.

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