Why it's now more likely you'll face coronavirus even if you're vaccinated against COVID-19

While leading vaccines are still providing high levels of protection from COVID-19, the delta variant is proving their toughest adversary yet.

Highly contagiousand likely capable of producing staggering virus levels inside the human body, the fourth major variant is driving Canada's fourth wave. It's also increasing the odds that more Canadians whether vaccinated or not will face thevirus in the weeks and months ahead.

"It's definitely going to be something we all encounter, at one point or another," said Dr. Zain Chagla, an infectious diseases specialist atMcMaster University in Hamilton.

"I think everyone, unless they're staying at home in a pure lockdown lifestyle, there's going to be exposures."

• Have a coronavirus question or news tip for CBC News? Email: Covid@cbc.ca or join us live in the comments now.

That means case counts will likely continue to rise for some time, including "breakthrough" infections among fully vaccinated individuals as the delta variant surges while vaccination rates slowly keep climbing.

But catastrophe isn'tinevitable.

WATCH |Canada needs to increase COVID-19 vaccinations, experts say:

Canada needs to increase COVID-19 vaccinations, experts say

3 years ago

Duration 1:59

Canada has edged ahead of the U.S. for per capita COVID-19 vaccinations, but experts warn the uptake needs to increase for better community protection.

Experts say that keeping some precautions in place would help protect vaccinated and unvaccinated alike, including millions of Canadian children, by preventing some potential transmission. And getting infected post-vaccination by this aggressive variant doesn't mean you'll actually wind up seriously ill or dying from COVID-19 in fact, the latest data shows it's still unlikely.

"You will get a large number of people who are unvaccinated getting quite sick, and even people who are vaccinated will get sick," said Dr. Andrew Morris, an infectious disease specialist with Sinai Health System in Toronto.

"How many people over the next few months will primarily depend on government action and public health measures."

Cases only among vaccinated would be 'manageable'

The stretch ahead, multiple experts who spoke to CBC News agreed, should be marked by a heightened sense of caution, regardless of whether you've had both shots.

That's not because every Canadian now faces the same base risk level, but because a delta-driven surge heightens the risk of infection for everyone a little if you're vaccinatedand potentially a lot if you're not.

"If all we had was a pandemic of the vaccinated," Chagla said, "it would be manageable."

Infections climbing among fully vaccinated individuals may still prompt alarm, even though those cases are expected and typically milder thanks to a variety of factors.

The delta variant itself may play a role. There's concern the same evolutionary properties that make it so skilled at infecting humans might also make it capable of evading some vaccination-based immunity.

Research suggests that vaccinated individuals clear a delta infection quicker than those who aren't protected, but it's still a more formidable foe. Another study estimated that being infected with thevariant leads to a 1,000 times higher viral load inside someone's nose whencompared to the original strain.

"That means every breath that we breathe, every cough that we cough, has that many more viruses that can transmit to the next person," said Sarah Otto, an expert in modelling and evolutionary biology with the University of British Columbia in Vancouver and a member of the independent B.C. COVID-19 Modelling Group.

What's also at play is simply a numbers game, multiple experts noted. If more people are getting vaccinated as more people are getting infected, a portion of those infections will inevitably be among that rising number of vaccinated individuals.

Take the situation in Iceland, for example, where more than 70 per cent of the total population is now fully vaccinated about 10 per cent higher than in Canada.

Between early July and early August, nearly eight in 10 domestic infections were among people who'd been vaccinated, an Icelandic health official told Reuters, adding that the figure shouldn't "come as a surprise" given the country's impressive vaccination rates.

More reassuring is that the high level of protection means that out of more than 1,000 people in isolation in early August, only 10 were hospitalized, and 97 per cent of those infected had mild or even no symptoms, government figures showed.

University of Ottawa epidemiologist Raywat Deonandan likened it to what happened when seatbelts became the norm.

"If 100 per cent of society wears seatbelts, the rate of fatalities by car crashes comes down, but amongthose that do happen, 100 per cent of those will be with seatbelts," he said.

"Doesn't mean seatbelts don't work."

WATCH |Data shows COVID-19 infections among fully vaccinated people are low:

Data shows COVID-19 infections among fully vaccinated people are low

3 years ago

Duration 1:55

While there are high-profile stories of fully vaccinated people getting infected, data shows they make up a small percentage of new infections. Experts say vaccines remains highly effective and will prevent people from getting very sick.

Serious breakthrough cases remain rare

If the delta variant finds its way to anyone who's both fully vaccinated and higher risk including the elderlyor anyone who's immunocompromised those cases are more likely to have dire outcomes.

Still, those serious breakthroughs remain rare, the latest data shows.

Since the start of Canada's vaccination campaign last December, infections have been overwhelmingly among unvaccinated individuals, at roughly 90 per cent, with less than one per cent among those who've been fully vaccinated.

While that federal data doesn't show how the trend is changing since the delta variant began its rise, Ontario figures from the last week show a larger portion of overall cases among those fully vaccinated though they're typicallypeople who are older and more vulnerable, according to provincial officials, andonly a handful of the serious infections requiring hospitalizationwere among that fully vaccinated group.

In the country's largest city, Toronto Public Health also recently reported that, since May 1, roughly 99 per cent of hospitalized COVID-19 cases with a known vaccination status were not fully vaccinated.

Of course, none of those figurescapture people who may be infectedbut have suchmild or non-existent symptoms that they never even get tested.

The early signals aren't surprising to vaccine experts, who havelong reminded Canadians that while this crop of vaccines areworking remarkably well at boosting people's immune responses, they've never offered perfect protection against an initial infection.

"It's like wearing rain boots in floodwaters. So long as the height of the boot is over the height of the water, your feet don't get wet so vaccines are great boots to keep your feet from getting wet with virus," Deonandansaid.

"The second that there's so much virus aroundthat the water leak slaps over into your boot, your feet are going to get wet. So it matters how much virus is circulating."

The reassuring bottom line is if you're young, healthyand fully vaccinated, the risk of falling seriously ill from delta remains low, even if cases continue to surge overall, said Morris, with Sinai Health System.

But as the delta variant continues to spread, it will find the vulnerable.

Dr. Theresa Tam, Canada's chief public health officer,noted last week that the number of people being treated for COVID-19 in Canadian hospitals rose by 12 per cent compared withthe week before, following recent increases in overall infections reported in multiple provinces.

That spike means Canada needs to use a variety of tools to keep the variant at bay, ranging from vaccine mandates to basic public health precautions, Morris said, particularly with schools set to welcome back millions of unvaccinated children.

"Masking works. Distancing works. Ventilation likely works," hesaid.

"All these things will make a difference. And this will do two things: reduce the number of people in the short term being infectedand buy more time for more people to be vaccinated."

Have questions about this story? We're answering as many as we can in the comments.