Study shows 'amazing' effectiveness of COVID-19 vaccine in preventing death, hospitalizations

"What it shows is that if you're vaccinated, you'll definitely be in the minority of people who end up with an infection, end up in hospital or end up dying."

Blair Crawford 4 minute read November 25, 2021

A file photo shows a nurse preparing a syringe of the Pfizer-BioNtech Covid-19 vaccine. FRED TANNEAU / AFP via Getty Images

Unvaccinated people account for 90.9 per cent of all COVID-19 hospitalizations in Ontario and 90.2 per cent of all deaths due to the disease, a new study from Public Health Ontario reveals.

Just 2.7 per cent of hospitalizations and 3.3 per cent of deaths in the province involved fully vaccinated people, the report shows.

“What it shows is that if you’re vaccinated, you’ll definitely be in the minority of people who end up with an infection, end up in hospital or end up dying,” said Dr. Gerald Evans, an infectious disease specialist at Queen’s University in Kingston.

“It’s the prevention of bad outcomes like death that the vaccine does an amazing job at, upwards of 90 to 95 per cent,” Evans said.

The study, released this week, gives the most detailed look yet at the effectiveness of the COVID-19 vaccines in Ontario at both preventing infections and limiting severe outcomes. It examines data from Dec. 14, 2020 — the day of the first vaccinations in Ontario — until Nov. 14, and includes the early stages of booster doses for the province’s most vulnerable citizens.

Over the 30 days prior to the report’s release, unvaccinated individuals were 4.8 times more likely to contract COVID-19 than fully vaccinated individuals, the study shows.

Unvaccinated people make up 91.7 per cent of all COVID-19 cases in the province while so-called “breakthrough cases” — infections in fully vaccinated individuals — account for just 3.8 per cent of cases. Less than 0.1 per cent of infections occurred in people who have received their third dose of vaccine, the report says.

The data are especially stark for people aged 60 and above. If you’re in that age group and unvaccinated, you are more than 16 times more likely to end up in hospital due to COVID-19 than someone who is fully vaccinated.

Those who’ve received their third dose — mostly seniors over age 70, the immunocompromised and their caregivers, at this point — account for less than 0.1 per cent of hospitalizations and less than 0.1 per cent of deaths.

While the vaccine is very good, it’s not a magic bullet, Evans cautioned. You can still get infected but likely won’t get as sick as you would if you hadn’t got your shot.

“Yes, you could get infected if you’re fully vaccinated, particularly if you’re hanging out with somebody who is infected and unvaccinated — and that’s what we’re beginning to see because there is more socializing going on since we’re all desperate for it,” he said. “But we know that the ultimate outcome is not going to be as bad.”

The study shows that of the 11,154,162 Ontarians who were fully vaccinated as of Nov. 14, just 17,596 had suffered a breakthrough infection.

Ontario reported 748 new COVID-19 infections on Thursday, with 419 of them in people who either aren’t vaccinated or whose vaccination status is unknown and 329 breakthrough infections. But looking at absolute numbers can be misleading, Evans said, because of the “base rate fallacy” where a tiny percentage of the huge pool of vaccinated people can still produce a few hundred cases.

“The rate of infections in vaccinated people is extraordinarily low … and you’re not taking into account that it was a much larger number that contributed to those infections.”

Ontario’s current vaccination rate is about 78 per cent of the entire population. Of the unvaccinated, children aged five to 11 make up about 30 per cent and they are now eligible to receive the pediatric dose of the Pfizer-BioNTech vaccine. Children under age four aren’t eligible for the vaccine and account for about 15 per cent of the unvaccinated.

“That leaves about 46 per cent or so who are people who are eligible for the vaccine, but aren’t vaccinated yet. Getting that population — the ones who are eligible and easily vaccinated — would go a long, long way,” Evans said.

In the meantime, the experience in Israel and some parts of the United States is providing good evidence to expand the third dose of vaccine to the over 50 group, he said.

“There’s a strong argument that 50 and older is where we want to look as we have enough vaccine,” Evans said. “Obviously, the most important thing is to get everyone vaccinated. That’s number one, But we’re reaching a threshold where trying to get that further bit is difficult.”

“Over age 50, you start to see a benefit to third doses.”


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