The majority of Canadians have already caught COVID-19: what impact for the future?

In British Columbia, researchers have analyzed nearly 14,000 blood samples from residents of the Fraser Valley since the start of the pandemic, to track antibody levels in the community. general population. They noted a significant change in the infection rate over the past few months.

Last April, the team of researchers from the British Columbia Center for Disease Control (BCCDC) and the University of British Columbia (UBC) estimated that about half of this population had already been infected with COVID-19. The latest data shows that this rate spiked in early spring and into the summer.

These findings were made public in a pre-published study (New window) this week, one of the co-authors of which is British Columbia’s Chief Medical Officer of Health, Dr. Bonnie Henry. This study, which has not yet been peer-reviewed, concludes that more than 60% of the general population has antibodies to SARS-CoV-2 due to prior infection.

Dr. Bonnie Henry is co-author of the study, which has not yet been peer-reviewed.

Photo: CBC/Ben Nelms

This really demonstrates the change registered, especially with the arrival of Omicron […] What we’re seeing is that people can get infected even when they’re vaccinated and that possibly leads to some immunityexplains Dr. Henry.

We do not know the level of antibodies necessary to be protected, adds Dr. Henry, but it shows rather well that the level of protection of the population against this virus is now very high.

The data, which is also grouped by age group, shows that Canadians under the age of 19 have the highest rate of infection, 70 to 80% d between them having been previously infected. This rate was around 60% in April.

The rate of prior infection is also on the rise in the adult population:60 to 70% of people aged 20 to 59 show signs of prior infection. This rate is around 40% for people over 60, an increase of 15% compared to March.

In one room, four residents in wheelchairs and a nurse.

During the first wave of COVID-19, many seniors living in care residences died from it.

Photo: Radio-Canada

We find that children are the most infected and the least vaccinated, while the elderly are always the most vaccinated and the least infected.says Dr. Danuta Skowronski, epidemiologist at the BCCDC and co-author of the study.

The most important conclusion I take from these latest data, adds Dr. Skowronski, is that the elderly are particularly dependent on vaccine protection as the fall of 2022 arrives and should therefore continue to be prioritized for booster doses of the vaccine.

The data shows a significant increase in infections after the arrival of the Omicron variant in Canada at the end of 2021. This raises questions about the impact of this significant immunity rate for the future at a time when Vaccines targeting newer, more contagious variants are administered across Canada.

Everything has changed over the past year and even more since the start of the pandemic, says Dr. Bonnie Henry. This tells me that now very few people are at extreme risk [sur la santé] as was the case when no one had immunity to the virus. We must take this information into account in our reflections.

A hand holds a syringe containing a Pfizer vaccine.

Pfizer’s new COVID-19 vaccine, approved by the European Medicines Agency on Monday, targets Omicron BA.4 and BA.5 subvariants.

Photo: Getty Images/David Ryder

Good news and bad news

This research report coincides with data from the Federal Task Force on Immunity to COVID-19 stating that in July nearly 60% of all Canadians had already been infected with the virus, a very significant compared to the previous year.

On Monday, the Task Force released data from Canadian Blood Services showing an increase in infections of nearly more than 30,000 among Canadians who donated blood in July. a jump of 50 to 54%, all ages combined.

It’s good news and bad newsnotes Dr. David Naylor, who led the federal inquiry into Canada’s response to the SARS outbreak in 2003 and is now co-chair of the federal COVID-19 Immunity Task Force.

A nurse vaccinates a person sitting in front of her.

By July, nearly 60% of Canadians had already been infected with the virus, according to data from the Federal Task Force on Immunity to COVID-19.

Photo: (Evan Mitsui/CBC)

The good news is that there is significant latent immunity from vaccination and previous infectionssays Dr. Naylor, adding that this hybrid immunity should limit the impact of COVID-19 as classes and in-person work resume.

This growth in the rate of hybrid immunity is a relative blessing, explains Dr. Naylor. This demonstrates that the virus is continuing to spread, meaning there are more people with “long COVID” symptoms that are of varying duration and severity.

Dr. Naylor points out that although symptoms are minor in the majority of those infected, there are many who still need to be in bed for several days before recovering and that COVID-19 continues to lead to death. a significant number of vulnerable people, a number that is expected to increase this fall and winter.

Light at the end of the tunnel?

The impact of this shift in Canadians’ immunity on possible new waves of COVID-19 remains to be determined, but for many vulnerable people, infection with the virus poses serious risks. These people continue to be at the top of the list of future vaccination campaigns.

We know who the most vulnerable to the virus areexplains Dr. Isaac Bogoch, infectious disease specialist at the Toronto General Hospital. Older people and people with already compromised immunity from other illnesses are obviously at greater risk. He adds that low-income people and members of racialized communities are also disproportionately affected by the virus.

We now have a baseline level of immunity in the population that protects everyone, concludes Dr. Bonnie Henry, including people who do not develop good immunity to the virus even after being vaccinated. The number of people who are at risk of becoming seriously ill from COVID-19 is therefore greatly reduced.

Giving a dose of the vaccine that targets the Omicron variant to an already well-vaccinated population helps create a community with hybrid immunity, which makes us much better prepared for potential future waves of infections.says Dr. Skowronski.

The Omicron variant of SARS-CoV-2, seen under an electron microscope.

The new bivalent vaccines target both the original SARS-CoV-2 virus and the Omicron BA.1 variant.

Photo: NIAID

For his part, Dr. Bogoch is cautiously optimistic about new bivalent vaccines and their long-term protection against future waves of the virus. He adds that these vaccines have not yet been proven.

That said, I prefer a vaccine that more closely targets the circulating virus, but I don’t know if that protection will be long-lasting, he says. Frankly, even the old vaccine protects against serious infection, hospitalization and death for a very long time. It’s true, he has proven himself, he is magnificent.

Dr. Henry says vaccination has been a game-changer in Canada and despite the high rate of infection and transmission of the virus, the situation is no longer the same.

I think it’s a difficult concept to understand because we’ve long told people that having COVID-19 is very, very serious, especially for immunocompromised people, she says. Now, given that there are so many people vaccinated and many have this hybrid immunity, the risk is really reduced for everyone.

With information from Adam Miller

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