What could the “COVID season” look like?


This is an excerpt from Second Opinion, a weekly roundup of health and medical science news. If you are not yet a subscriber, you can do so by clicking on here.


As wave after wave of COVID-19 crashes upon us, the hope is that we will eventually reach a point where the seasonality of the virus will make the pandemic easier to predict and overcome.

But with new variants emerging that are highly contagious and causing outbreaks around the world at different times – will we soon reach a regular “COVID season”?

The pandemic has not followed a well-defined pattern in Canada, with waves hitting erratically across the spring, grave and Winter over the past two and a half years, largely due to the lifting of public health measures and new variants threatening immunity from vaccines and previous infections.

Different variants also caught countries off guard at unexpected times (and sometimes missed them entirely), making it increasingly difficult for us to predict when and where the waves of COVID would hit next.

“Let’s be honest, it’s the virus that’s in control here, not us,” said Dr. Michael Gardam, infectious disease physician, medical director of infection prevention and control at Women’s College Hospital in Toronto and CEO of Health PEI

“We are completely at the mercy of all the random evolutionary events that happen and it’s really hard to predict.”

Different countries, different waves

Canada currently has a nasty mix of Omicron sub-variants – including BA.1, BA.2, BA.2.12.1 and BA.2.3 – fueling an ongoing sixth wave after public health measures were largely lifted , despite more than 80 percent Canadians vaccinated and almost half of the population infected.

The United States avoided a major wave of BA.2 until the end of last month, but BA.2.12.1 quickly becomes the dominant strain to almost a third of new cases, while Europe also faces a increased BA.2 subvariants and the emergence of BA.4 and BA.5.

And this, despite relatively high vaccination rates, with just over two-thirds double vaccinated in the United States and more than 70 percent in Europe, and even higher levels of previous infection.

More than half of Americans had been infected with the virus in February, according to new data from the US Centers for Disease Control and Preventionwhile EU officials have reported between 60 and 80% of the European population have had COVID-19.

“It’s going to get harder and harder to compare countries…and honestly, even before that it was a bit difficult,” said Deepta Bhattacharya, an immunologist at the University of Arizona.

“The Alpha wave really nailed the UK and it hasn’t really nailed it here and I don’t know why. It was definitely introduced here and it didn’t spread to the same extent and I don’t know not why. So there are all kinds of things that make it very difficult to understand and to predict.”

People walk through Chinatown in Toronto in March 2021. Canada currently has an unpleasant mix of Omicron subvariants fueling an ongoing sixth wave after public health measures were largely lifted. (Evan Mitsui/CBC)

Population immunity could dampen future waves

Another hard-to-predict factor is how population immunity will change – and whether past infections and high vaccination rates will protect or wane over time.

Tulio de Oliveira, director of the South Africa Center for Epidemic Response and Innovation, said South Africa had a high level of population immunity, with more than 90% estimated to have been previously infected, vaccinated or both.

“That’s one of the reasons we think the big Omicron wave we had didn’t translate to a very high number of hospitalizations and deaths,” he said.

“And BA.2, although emerging and continuing to dominate all infections in South Africa, did not translate to an increase in infection, which was very different in Europe, where they had a surge BA.1 followed by a wave BA.2.”

This double whammy from Omicron’s BA.1 and BA.2 also hit Canada hard, fueling a devastating fifth wave late last year that subsided just as BA.2 sparked a sixth smaller wave in April – but it also increased our population levels. immunity.

“It gives you the impression that the more people who are infected and vaccinated, the better you resist,” Gardam said.

“The hope is that it starts to become like the other coronaviruses that infect us every year and cause colds… and eventually it’s hard enough for the virus to come up with something so new that you never have one seen a game before.”

As a result, Omicron and its subvariants completely changed the landscape of immunity in Canada over the past few months.

Previously, Canada was more in line with a country like South Korea given our high vaccination rates and previously low previous infection levels, de Oliveira said, with much of the country seeing relatively low levels of COVID while throughout the pandemic.

With Omicron, we were more like countries like South Africa and the United States with much higher levels of population immunity – but our high vaccination rate protected us.

“What this means is that potentially as new variants and sub-variants of Omicron emerge … this may result in a relatively high number of infections, but potentially not a very high rate of hospitalization and death,” he said.

“Look at the first wave, it was a very small wave but there were a lot of hospitalizations,” Gardam said. “Then Omicron finally hit and the spike in infections was insane, but the death rate was never as high as it was in previous waves, so we’re trying to tackle that better.”

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Gardam said the difference between provinces like Prince Edward Island and Ontario throughout the pandemic is that the Maritime provinces that have taken a COVID zero approach had little pre-existing immunity over the past two years.

But when Omicron struck in December, it exploited the province’s population’s lack of immunity.

“It was like bang, here it is,” he said. “And it’s still going through the population and yet we had stricter measures than Ontario and other provinces, but they went through all these different waves that we didn’t have.”

How will we get to “COVID season” with variants constantly emerging?

While it’s unclear whether new levels of Canada’s population immunity and consistently high vaccination rates will fend off future waves of the virus and bring us closer to seasonality, there are early hints from other countries. that we might be able to better predict waves in the future.

Tom Wenseleers, an evolutionary biologist at KU Leuven University in Belgium, said the Twitter that South Africa is beginning to show signs of seasonality with COVID, which could look like “a large wave every six months with significant mortality and morbidity”.

“The impact on the health system of both BA.2.12.1 and BA.4 and BA.5 is really not yet clear. They will cause waves of infections, of course, but the impact on hospitalizations and the expected mortality cannot yet be estimated at this time,” he told CBC News.

“Early data seems to suggest similar severity to the original Omicron in terms of case hospitalization rates…but it really is too early to infer that.”

de Oliveira, who led the research team that identified the BA.4 and BA.5 subvariants in South Africa, said reduced immunity to infection and vaccination may be a factor. of their spread.

“The only thing that may play a role in that is just the timing of the BA.1 wave, and that’s why we’re looking at the data very carefully,” he said.

“We are talking about three or four months after the peak of BA.1 and we know that it is around three or four months that the immunity of the population begins to decline.

A new pre-publication study co-authored by de Oliveira, which has not yet been peer-reviewed, suggested that there may be “growth advantages” for BA.4 and BA.5 over BA.2 in South Africa. South that could potentially trigger another wave, but whether it will happen there or in other countries remains to be seen.

And other variants are probably on the horizon.

“That appears to be the behavior of SARS-CoV-2 and I think we shouldn’t be shocked when we see another variant,” said Alyson Kelvin, a virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious Disease Organization. in Saskatoon.

“But also continue to plan for them, unfortunately, which I think impacts our vaccination strategies… as you roll [an updated vaccine] there is a new variant.”

People brave the snow to line up for COVID-19 testing in early January in Vancouver. The chaotic pattern of COVID waves in Canada has yet to show major signs of seasonal transmission, but there are indications that we could eventually get there. (Ben Nelms/CBC)

Although the chaotic pattern of COVID waves in Canada has yet to show major signs of seasonality, there are signs that we are heading towards it.

“There is always a seasonality associated with COVID. That’s not to say it’s a perfect fit, but of course there are times during the colder months in Canada when we see more cases,” said infectious disease physician Dr Isaac Bogoch. at Toronto General Hospital.

“Let’s hope this surge subsides and we have a great summer ahead of us…but can this be disrupted by a highly transmissible variant? Maybe. It’s possible.”

Gardam said if we take a long-term look at other viruses like H1N1, the flu strain that started the 1918 pandemic, we can expect COVID-19 to be circulating for many years now that the eliminating it completely isn’t possible – but it probably won’t be. cause anywhere near the same level of disease.

“I have to assume that in 20 years there will be remnants of this coronavirus around which we will be regularly infected,” he said. “But that’s not a big deal anymore.”