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COVID-19 vaccines reducing spread, severity despite breakthrough cases, experts say


While the number of COVID-19 cases is steadily increasing in individuals who are fully vaccinated against the virus, experts say the data shows that vaccines continue to work in reducing transmission and preventing severe infection.

A breakthrough infection is when an individual tests positive for COVID-19 more than 14 days after completing the recommended series of a two-dose COVID-19 vaccine.

In Ontario, 10,840,016 people were said to be fully vaccinated as of Oct. 17. According to Public Health Ontario, 12,694 of these individuals tested positive for COVID-19, in addition to 20 people who had received a third dose or booster shot.

In the last two weeks, 1,760 Ontarians reported breakthrough infections, accounting for roughly 35 per cent of the provinces total infections during this period.


Dr. Dale Kalina, an infectious disease physician at Joseph Brant Hospital in Burlington, Ont. told that breakthrough cases are expected. He explained in a telephone interview Friday that, as vaccination rates increase, so will the number of breakthrough cases, simply because there are fewer unvaccinated people.

"If 100 per cent of the people were vaccinated here in Ontario, then 100 per cent of the cases would also be in vaccinated individuals," Kalina said. "But what we would see is a far lower number of people who were having the disease and also having, of course, severe disease."

Breakthrough cases have also been steadily rising in other parts of Canada, including in British Columbia, Saskatchewan and Manitoba.

The Public Health Agency of Canada (PHAC) reports that there have been 48,555 coronavirus cases in fully vaccinated individuals and 47,230 infections in those who are partially vaccinated as of Oct. 9. This makes up roughly 12 per cent of Canada's total COVID-19 cases since the start of the pandemic.

However, the rate of hospitalizations and death are still considerably higher among unvaccinated people than the fully vaccinated population.

Kalina noted that it is not only important to look at the number of fully vaccinated people testing positive for the virus, but also their severity of infection, whether mild or severe.

While some Canadians may be more prone to a breakthrough infection, such as seniors, those living in long-term care homes, and people with underlying medical conditions, Kalina said even healthy individuals can still test positive for COVID-19 after being vaccinated. However, their infections likely won't be severe.

Kalina added that many breakthrough cases are asymptomatic and would otherwise go unnoticed, but were likely reported in provincial case counts because the individual works in a setting that requires daily COVID-19 testing, or they were admitted to a hospital for another reason, such as a broken bone, and were revealed to be infected.

Kalina said it is also important to look at the number of infected individuals who are currently in ICUs to get a full picture of who COVID-19 is predominantly affecting in Canada and how.


A new study of 621 people in the U.K. with mild COVID-19 infections found that people who are fully vaccinated can still pass the infection on to vaccinated and unvaccinated household members.

The study, published Wednesday in peer-reviewed medical journal The Lancet, found that the infectiousness of breakthrough infections in fully vaccinated people was similar to unvaccinated cases, with 25 per cent of vaccinated household contacts testing positive for COVID-19 compared with 38 per cent of unvaccinated members.

While infections in vaccinated patients cleared quicker than in those who are unvaccinated, the study noted that both infections resulted in a "similar peak viral load," which is when people are considered to be at their most infectious.

Kalina says the study highlights the significance of using vaccines in combination with other public health measures, such as masking and social distancing, to fight COVID-19.

"Those public health measures in addition to vaccination is why we have a relatively low level of circulating virus as contrasted to regions like… the United Kingdom," he said.

While the data shows that the number of post-vaccination cases declines as time from vaccination increases, Kalina noted that vaccines are not 100 per cent effective, nor have they ever promised to be.

Despite the term "breakthrough" making it seem like the vaccines failed, Kalina stressed they do work.

"The important thing to recognize is that we know that the vaccines themselves don't prevent all viruses, and they don't prevent transmission. We know that the vaccines… reduce the risk of transmission, they dramatically reduce the risk of disease, especially severe disease, and almost entirely eliminate the risk of death," Kalina said.


Infectious disease expert Dr. Isaac Bogoch says breakthrough infections are normal, and they were reported in all of the vaccine studies and clinical trials.

"We've known from the very beginning, we've known even before Delta variant emerged, that people can get breakthrough infections," Bogoch said in a telephone interview Friday. "So it should come to no one's surprise that people can still get COVID-19 if they're vaccinated."

However, Bogoch said the COVID-19 vaccine should start being looked as a three-dose vaccine series, not a two-dose regimen.

"The third dose that many people will be getting in the coming months will likely reduce the risk of people getting COVID-19 and will likely further reduce the risk of severe illness even in vaccinated individuals where we already have a much lower risk of severe illness," Bogoch said.

Canada has already began providing third doses to elderly people who live in long-term care facilities and for those with compromised immune systems, however, Bogoch said booster shots need to be rolled out quicker to other vulnerable groups to maintain effectiveness.

"When we look at all the people who are vaccinated and getting infected… there are groups who are at greater risk. We've got to really focus our attention on protecting those populations," Bogoch said.

The National Advisory Committee on Immunization (NACI) expanded eligibility guidelines for booster shots on Friday, recommending that mRNA boosters also be given to Canadians who have received two doses of the Oxford-AstraZeneca vaccine, adults over the age of 70, front-line health-care workers with a short interval between their first two doses, and people from Indigenous communities.

Bogoch noted that the best way to protect oneself and others continues to be getting vaccinated against the virus.

According to data tracked by, more than 88.8 per cent of Canada's eligible population has received one dose of a COVID-19 vaccine and 84.1 per cent are fully vaccinated, as of Oct. 29. So far, 407,024 Canadians have received a third, booster shot of a COVID-19 vaccine.

Since the pandemic began, there have been more than 1.7 million confirmed cases of COVID-19 in addition to more than 28,900 deaths.

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