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A man walks by a sign for a COVID-19 testing centre in Montreal on Oct. 10, 2021. COVID-19 cases and wastewater levels are increasing again in several parts of the country, raising concerns that another wave has already begun.Graham Hughes/The Canadian Press

There are a lot of unknowns about how a new COVID-19 wave will play out in Canada in the coming weeks, but clinicians and scientists say many of the lessons learned from previous ones can help mitigate its effect.

Even though the virus continues to change, some of the basic public-health advice still applies, said Jeff Kwong, a professor of family medicine and public health at the University of Toronto.

“Ventilation, masks and vaccines all still work to varying extents and for various things,” Dr. Kwong said.

In several parts of the country, COVID-19 cases and wastewater levels are increasing again, raising concerns that another wave has already begun.

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Data from the Ontario COVID-19 Science Advisory Table show that several indicators in that province, including test positivity, wastewater levels and hospitalizations, suggest the virus is on the rise. Case counts in Quebec are climbing. And according to the federal wastewater surveillance data, last updated on July 5, six out of 22 recorded sites across the country showed a possible increase in COVID-19 levels in wastewater, compared with the seven days previous. These include sites in Halifax, Charlottetown and Vancouver.

“It’s a question of how big and how serious, but it’s definitely a wave,” said Tania Watts, an immunologist at the University of Toronto.

One factor that will shape how this wave turns out is the amount of immune protection the public has against the virus.

New analysis of blood testing data by Canada’s COVID-19 Immunity Task Force, released on Wednesday, suggested that the proportion of Canadians who had antibodies to SARS-CoV-2 infection, the virus that causes COVID-19, rose 45 per cent. This suggests more than 17 million Canadians were infected by the Omicron variant. Prior to the introduction of Omicron, about 7 per cent of the population had infection-acquired antibodies to SARS-CoV-2, the task force said.

Meanwhile, close to 82 per cent of the total population is considered fully vaccinated against COVID-19, and nearly 60 per cent of those ages 12 and older has had at least one additional dose, according to federal data.

However, BA.5, the new variant poised to become dominant in Canada, is able to evade immune protection. That means everyone who caught Omicron is now susceptible to reinfection again, Dr. Watts said.

Research led by University of Toronto scientist Igor Stagljar backs this up. Using a new antibody test he and his team developed, they found immune protection acquired by a vaccine or a prior infection lasts only four months against the new variants, BA.4 and BA.5.

“If someone had COVID at the beginning of this year or if someone got vaccinated at the beginning of this year, this means that we have zero – almost zero – protection in the form of neutralizing antibodies,” against the new variants, said Dr. Stagljar, a professor at the Donnelly Centre for Cellular and Biomolecular Research at the Temerty Faculty of Medicine.

Additionally, some of the medications used for COVID-19 have become no longer effective with the arrival of new variants, said James Heilman, an emergency physician in Cranbrook, B.C. For example, several months ago, he was using sotrovimab, an injectable antibody, to treat patients with severe COVID-19, but with the onset of Omicron, the treatment no longer works.

It is also now becoming clear that Paxlovid, once thought to be a potential panacea, is only useful for those at high risk of severe illness, Dr. Heilman said.

In spite of these new challenges, however, the main way people contract COVID-19 has not changed.

“The disease has been airborne from the start,” said Dr. Heilman, editor of Wikipedia’s medical content.

That means high-quality masks still work to reduce the risk of infection, not only from COVID-19 but other respiratory viruses, Dr. Kwong said. Cloth masks are better than nothing, he said, but emphasized N95 or KF94 respirators are best.

The now-familiar refrain that gathering outdoors is safer than indoors still applies, Dr. Watts said. Same goes for the idea that small groups are safer than big crowds; the odds of catching COVID-19 in a room with 1,000 people remains higher than in a room of 10 people, she said.

And even though contact with infected surfaces may not be the main route of transmission, handwashing is still a good idea, Dr. Watts said.

But certain health messages should now be modified or scrapped, they said.

Staying two metres apart from others will not necessarily keep people safe, Dr. Kwong said. If they spend time in an enclosed space where many people are generating a lot of small particles, transmission can occur, even when everyone is spaced apart, he said.

Current guidelines, which call for self-isolating at least five days after the onset of symptoms or a positive test and masking when in public from days six to 10, could also use revision, Dr. Watts said. In some cases, the virus can be shed after day five, so she recommends taking a rapid antigen test after five days, and staying home longer if the test is positive.

Dr. Heilman added that people should not assume they are free of COVID-19 just because they test negative on a rapid test. It can several days of symptoms before people get a positive test, he said.

Moreover, having two vaccine doses should no longer be considered fully vaccinated, but instead, it should be considered a three-dose vaccine, Dr. Watts said. Even though vaccines don’t completely protect people against infection, they do provide good protection against severe illness and reduce the risk of long COVID, she said.

Given how quickly immunity declines, however, Dr. Stagljar suggested Canadians may expect to need an additional dose every four to five months. A test that measures neutralizing antibodies, like the one he and his team have developed, could help determine when people need a booster dose, he said.

Ultimately, it’s a mistake to think that efforts to stop the spread of COVID-19 can be abandoned just because it’s not killing or seriously sickening as many people, Dr. Watts said, adding that infections allow the virus to mutate further.

“We all have a societal contribution not to spread COVID and make the overall pandemic worse, and also obviously affect the vulnerable,” she said.

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