Health·Second Opinion

Want to cut your risk of serious COVID-19? New data shows vaccines are hitting the mark

A growing body of global data shows that leading COVID-19 vaccines significantly reduce your risk of falling seriously ill or dying if you wind up infected with the coronavirus. But plenty of people still remain at a higher risk.

Unvaccinated 36 times more likely to be hospitalized for COVID-19, new data shows

A growing body of data shows leading COVID-19 vaccines significantly reduce your risk of falling seriously ill or dying if you're infected with the coronavirus. But plenty of people still remain at a higher risk. (Getty Images)

This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed to subscribers every Saturday morning. If you haven't subscribed yet, you can do that by clicking here.

Vaccines work. Before we move on to some caveats, let's start with that.

A growing body of global data shows that leading COVID-19 vaccines significantly reduce your risk of falling seriously ill or dying if you wind up infected with the coronavirus.

That's particularly the case when they're used alongside other public health measures to prevent infections from happening in the first place — and even when faced with the hyper-contagious delta variant.

They don't work perfectly, of course — and we'll get to that in a bit — but really, really well.

The latest Canadian data released on Friday shows that from late July to late August — while the more-contagious delta variant was circulating widely — unvaccinated individuals were 36 times more likely to be hospitalized for COVID-19 than those who were fully vaccinated.

South of the border, a new report from the U.S. Centers for Disease Control and Prevention featuring data from early April to mid-July showed that people who were not fully vaccinated were at least 10 times more likely to be hospitalized or die of COVID-19 than those who were fully vaccinated.

And in the U.K., the latest public health report shows that both the vaccinated and unvaccinated are getting infected — and infection rates in certain age groups are even higher among fully vaccinated individuals.

But when it comes to the COVID-19 death toll, that's where things noticeably shift: Unvaccinated individuals had a significantly higher risk of dying after being infected with the virus than vaccinated individuals across every age category.

"It's much harder right now, I think, to try and say that vaccines don't work," said Jason Kindrachuk, an assistant professor in medical microbiology and infectious diseases at the University of Manitoba in Winnipeg.

"So unless you're basically kicking your feet and stomping really loudly, your message is going to get drowned out pretty quick just by the data we're seeing on a daily basis."

What vaccines do — and what they don't

But there is plenty of foot-stomping from some — and quiet concern from others — as reports of vaccines seemingly not working tend to dominate the headlines, be it debates over booster shots to combat the possibility of waning immunity or reports of post-vaccination infections.

Even the sky-high efficacy rates of mRNA vaccines during clinical trials left a little window of imperfection — and those trials happened long before this virus evolved to replicate quicker, spread faster and infect even more unsuspecting human hosts.

It's helpful to remember that in day-to-day life, there's no magic way to avoid getting infected, save for locking yourself in a bunker. Layering protections such as masks and physical distancing seems to help, but as one vaccine expert told this reporter previously, it's worth noting that a vaccine doesn't provide that same kind of physical barrier to prevent someone from coughing or sneezing your way.

In other words, under the right circumstances — whether you're vaccinated or not — SARS-CoV-2 might find its way inside your body.

It's what happens next that's key.

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A COVID-19 testing site at Evraz Place in Regina on Thursday. (Matthew Howard/CBC)

At a basic level, vaccines train your immune system to recognize a specific threat. If you're vaccinated, your body already has a heads-up about the virus, and if your immune system is functioning well, you can begin to fight it off. If you're not vaccinated, you're caught off guard, making it more likely you'll lose that battle.

So why do some fully vaccinated, highly protected people still wind up getting seriously ill, or even dying, from COVID-19?

"The people that are, relatively speaking, most at risk of having something bad happen after a breakthrough infection are the same people that are at highest risk of having something bad happen for any infection and for COVID-19," said Deepta Bhattacharya, an immunologist at the University of Arizona in Tucson.

Bhattacharya says that includes people who are immunosuppressed or those who are being treated for autoimmune disorders or certain types of cancer.

"Those are the kinds of things that would put you at pretty high risk of not responding that well to the vaccine," he said. "And as a result, being at high risk of severe disease."

Emerging hints about who's more at risk

Most public data doesn't actually tell you much about the age or health of people suffering from those "breakthrough" infections after full vaccination, but there are emerging hints about who's typically showing up at hospitals.

Research published on Tuesday in the Lancet looked at 969 patients who were admitted to a Yale New Haven Health System hospital in Connecticut from late March to early July and wound up testing positive for SARS-CoV-2 — whether or not they were being treated for COVID-19 or another ailment.

During the study months, only 54 of the admitted patients were fully vaccinated. Nearly half didn't show symptoms of COVID-19, despite testing positive for the virus, and had come to the hospital to treat another, unrelated diagnosis.

Out of those actually showing symptoms, roughly a quarter had severe or critical illness, including three deaths — and of that seriously ill group of fully vaccinated patients, the researchers found the median age was about 80 years old, with people experiencing various pre-existing health issues such as obesity, cardiovascular disease, cancer, diabetes or some kind of immunosuppressive drug or condition.

"Those are the people that are getting breakthrough infections: older, predominantly with underlying medical comorbidities," said Dr. Isaac Bogoch, an infectious diseases specialist with the University Health Network in Toronto.

WATCH | Specialist explains who's getting serious breakthrough infections: 

Infectious diseases specialist on who's getting serious breakthrough infections

2 years ago
Duration 0:55
Toronto-based infectious diseases specialist Dr. Isaac Bogoch says new data from Public Health England shows the bulk of those getting serious breakthrough COVID-19 infections after full vaccinations are the elderly, suggesting that group may benefit from booster shots.

It's a small study at one hospital, but headline-making Israeli data over the summer also showed a rise in country-wide hospitalizations after the delta variant began circulating while restrictions were lifted, even among those fully vaccinated.

In late August, a Reuters report noted, about half of the country's roughly 600 COVID-19 hospitalizations were people who had two rounds of Pfizer-BioNTech shots — worrisome at face value, but still a rare event out of more than five million fully vaccinated residents.

The majority of those seriously ill patients were seniors, had other chronic illnesses or were on immunosuppressive drugs, and were among the first in the country to be vaccinated more than five months prior, according to a number of medical professionals who helped put the raw tally in context.

"Yes, there are breakthrough infections. But when you look at that, as compared to the overall number of vaccinations that have been presented, it's a tiny population that we're seeing," stressed the University of Manitoba's Kindrachuk.

"In many cases, people see breakthrough infection, and now they equate that as being a normal event amongst people that are vaccinated — all the data certainly suggests the opposite to us."

In the heavily vaccinated U.K., officials are even urging the public to interpret their latest vaccination and infection data with caution.

In the context of very high vaccine coverage in the population, "it is expected that a large proportion of cases, hospitalizations and deaths would occur in vaccinated individuals," simply because a larger proportion of the population are vaccinated than unvaccinated and no vaccine is 100 per cent effective, the latest report reads.

"This is especially true because vaccination has been prioritized in individuals who are more susceptible or more at risk of severe disease."

Countries turning to booster shots

Against this backdrop of post-vaccination infections, there's a debate over whether to offer additional vaccine doses to give people's immune systems an extra boost — and, if so, who should actually get them.

In Canada, the recommendation — at least so far — is to give third shots to certain people with weaker immune systems.

Canada's National Advisory Committee on Immunization released recommendations on Friday to provide a third vaccine dose to some cancer patients, transplant recipients and people with advanced HIV infections or serious immunodeficiencies.

"Individuals who are moderately or severely immunocompromised, including those receiving immunosuppressive therapies, are more likely to have a lower immune response to only two doses of COVID-19 vaccines," Dr. Theresa Tam, Canada's chief public health officer, noted in a statement released on Friday.

WATCH | Waning immunity sparks debate about need for COVID-19 booster shots: 

Waning immunity sparks debate about need for COVID-19 booster shots

2 years ago
Duration 2:04
Recent studies show a drop in effectiveness for COVID-19 vaccines, but the lack of information about how severe breakthrough cases were has sparked a debate about whether booster shots are necessary.

Bhattacharya of the University of Arizona said there's "widespread consensus" about offering extra shots to those groups, with emerging evidence suggesting that seniors should be given additional doses as well.

Bogoch agreed that any booster shot programs should target both the elderly and immunocompromised but not the general public in Canada just yet — despite countries such as the U.S. and Israel already offering third doses to younger residents as well.

"It doesn't make any sense. You see virtually no serious, severe cases in those younger cohorts," Bogoch said. "And why would you? What would be the benefit of giving a vaccine there?"

These vaccines aren't meant to stop the coronavirus from entering and replicating in your body, he explained, though that's obviously a best-case scenario.

Instead, Bogoch said, COVID-19 vaccines are ultimately meant to prevent serious infection, hospitalization and death — "and they're still doing that."

Not perfectly — and not for everyone. But by and large, they work.


Lauren Pelley

Senior Health & Medical Reporter

Lauren Pelley covers health and medical science for CBC News, including the global spread of infectious diseases, Canadian health policy, pandemic preparedness, and the crucial intersection between human health and climate change. Two-time RNAO Media Award winner for in-depth health reporting in 2020 and 2022. Contact her at:

With files from Adam Miller

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