TORONTO – It might sound like bad news, but it’s actually good: most Canadians have contracted Covid-19 since Omicron and its highly contagious sub-variants first appeared. Virtually two out of three Canadians have caught the coronavirus. And the news is good because, according to experts, this, added to the massive vaccinations made, generates broad immunity or, in any case, greater protection against the more serious forms of Covid. 

The study was led by the team of the Center for Disease Control and Prevention (BCCDC) and University of British Columbia, which analyzed nearly 14,000 blood samples in the Lower Mainland during the pandemic to monitor population antibody levels, finding a huge change in the number of infections in recent months.

The team previously found that nearly half of the population had caught Covid in April, but new data suggests that the number continued to skyrocket during the spring and summer, reaching over 60% of the population. “What we are seeing now is that people have had an infection in addition to being vaccinated and this leads to a level of potential immunity,” British Columbia Provincial Health Officer Dr Bonnie Henry told CBC. “We don’t know how many antibodies you actually need to have to be totally immune, but the current situation gives us the feeling that we now have a very high level of protection of the population against this virus.”

The data is also broken down by age groups and reveals that the highest level of infections is in Canadians under 19, with at least 70-80% of young people now showing evidence of a previous infection, compared to around two/thirds in April.

But adults are also seeing an increase in infections, with at least 60-70% of those aged 20 to 59 now showing evidence of a previous infection and around 40% of Canadians over 60, compared to 15% in March. “What we have observed is that children currently appear to be the most infected and least vaccinated, while the elderly remain the most vaccinated and least infected,” says Dr Danuta Skowronski, head of epidemiology at the BCCDC (British Columbia Center for Disease Control) and co-author of the study. “The main starting point for me and my colleagues is that seniors are particularly dependent on vaccine-induced protection alone, and as we are entering the fall, they should be prioritized for additional booster doses.”

“We are at a completely different point from where we were a year ago and, in particular, at the beginning of the pandemic,” added Dr. Henry. “There are very few people now who are at as extreme risk as they were in the beginning when we had no immunity in anyone.”

The research also coincides with national data from the federal government’s Covid-19 Immunity Task Force, which suggests that nearly 60% of Canadians coast-to-coast had already been infected before July – a huge increase in the past year.

The task force also released new surveillance data from Canada Blood Services on Monday that showed an increase in Covid-19 infections among the more than 30,000 Canadians who donated blood in July, jumping from 50 to 54 percent across all brackets of age. But in younger age groups that rate, again, is much higher, particularly among those between 17 and 24 who had a previous infection rate of over 71%.

According to Dr. David Naylor, who led the federal investigation into Canada’s national response to the 2003 SARS outbreak and now co-chairs the federal government’s Covid-19 Immunity Task Force, “the upside is that there is a lot of background immunity from vaccines and past infections,” he said, noting that such combined “hybrid immunity” should help “limit the impact of Covid in the coming months.”

“It’s a turning point, now let’s protect in priority who is at risk”

“The people who are really susceptible to serious illness are very, very few now”: speaking is the British Columbia Provincial Health Officer, Dr. Bonnie Henry. It is therefore easier to identify who to go to protect, even in the event of a new wave, says Dr. Isaac Bogoch, infectious disease doctor at Toronto General Hospital. “We know who is most vulnerable to Covid. Obviously, we know that it is the elderly and people with underlying medical conditions who put them at the greatest risk,” Bogoch said, noting that low-income and racialized communities are also affected in a disproportionate way. “So many people have been infected in the last six months … if you add to that the high levels of vaccination, at least with the first and second doses, there is room for further improvement with booster doses … but we already have significant protection at the community level.”

Bogoch says he is “cautiously optimistic” that the updated “bivalent” vaccines, which target both the original virus and Omicron’s first variant, BA.1, will provide lasting protection against further spread of the virus, ” but their impact has yet to be seen in the real world. That said, I would rather have a vaccine more suited to the virus in circulation now than not, but I don’t know what the duration of protection will be,” he said, adding that “also the old vaccine has very long-lasting protection against severe infections, hospitalization and death. It does, it stands over time, it’s fantastic. We hope to maintain that protection against serious infections and we will regain lasting protection against infection.”

Dr Danuta Skowronski, head of epidemiology at the British Columbia Center for Disease Control (BCCDC), says the results of the study conducted by her center give important indications on where to target future “boosters”: older Canadians, immunocompromised groups and vulnerable categories are the main concern. “Superimposing the increased infection on an already highly vaccinated population is contributing to more robust hybrid immunity and this is really a silver coating. It puts us in a much better position to deal with any new waves,” she said. “Which is why I say that the sense of urgency of additional doses can be alleviated for most of the population who have accumulated that combination of vaccines and infection-induced exposures that contribute to hybrid immunity.”

Pic by Michal Jarmoluk from Pixabay