COVID keeps evolving, but so does our immunity. Are we now at a 'stalemate' with this virus?

After billions of global COVID-19 infections, millions of deaths, and countless lives upended by long-lasting health impacts, we've finally hit a point in this pandemic where SARS-CoV-2 isn't the fearsome pathogen it used to be.

Once thought to kill up to 20 per cent of those infected in the early days of 2020, COVID's destructive potential is now being throttled by widespread immunity and regularly-updated vaccines.

Even so, this ever-evolving virus is with us to stay. It still causes rolling waves of infections, much like seasonal influenza or the common cold. It's found across the globe, in animal populations from deer to cats to mink. And it keeps mutating to better dodge our front-line immune defences and re-infect us over and over. 

We didn't stamp it out, like many hoped. Nor did it destroy everyone's immune systems, like some feared.

Instead, as University of Arizona immunologist Deepta Bhattacharya puts it, we're now in a "stalemate" with SARS-CoV-2.

"It's definitely not what it was in those awful days of early 2020. There's no doubt about that. And so far, we haven't really seen anything that would suggest that there's any possibility we'd go back to that," he added. 

"I mean, there's almost no one left who doesn't have some form of immunity to the virus, whether it's through a vaccine, infection, or some combination of both."

A new study, published today in the Canadian Medical Association Journal (CMAJ), highlights that level of immunity built up across the Canadian population.

Exposure to this virus, whether through vaccination or infection, means three-quarters of the country had detectable antibodies by March 2023, the research team found. (Those antibodies can wane and become tougher to detect over time — and don't represent longer-lasting immune memory — which means the level of population immunity to protect people against dire outcomes might be even higher.)

The scientists analyzed more than 700,000 individual samples, said one of the study's authors, Dr. David Buckeridge, the scientific lead for data analytics at the COVID-19 Immunity Task Force, and a professor in the School of Population and Global Health at McGill University in Montreal. The findings showed early vaccination efforts fuelled an immunity boost, though the major jump followed the arrival of the highly-contagious Omicron variant.

"These antibodies are a pretty good window on immunity," Buckeridge said. "It shows us what we've been through and how the population responded, both in terms of how quickly we were vaccinated, the impact that had, but then also when new variants arrived, how that managed to escape the vaccination and cause that rapid rise in infection."

The new Canada-wide study follows earlier research in B.C. which also suggested rising levels of antibodies in that province by the summer of 2022.

Researcher Dr. Danuta Skowronski, the epidemiology lead for influenza and emerging respiratory pathogens at the B.C. Centre for Disease Control, said the CMAJ paper further reinforces those provincial findings.

"This virus is established in the population, it's not going away, we're not going to drive it back into nature — we are long past that hope," she said. "What we are aiming for now is preventing severe outcomes from infection."