What do Ontario’s breakthrough infections teach us about the COVID-19 vaccine?

The Ontario government has recently been reporting the number of breakthrough COVID-19 infections in fully vaccinated people, as part of its daily data collection — and the percentage has been sitting around 20 per cent.

On Aug. 26, 678 new cases of COVID-19 were reported in the province and among those infected individuals, 141 were fully vaccinated. Out of that data, 395 were unvaccinated, 82 were partially vaccinated and 60 have an unknown status. 

As well, Ontario reported that out of all the people who are currently in hospital due to COVID-19, but not in ICU, 137 are unvaccinated, 14 are partially vaccinated and 31 are fully vaccinated. 

Of those in ICU, 89 are unvaccinated, nine are partially vaccinated and 10 are fully vaccinated. 

Tania Watts, a professor of immunology at University of Toronto, who is also a member of the Ontario COVID-19 Science Advisory Table, said these breakthrough rates are “not unexpected.”

In an email to Metroland, Watts said the rates actually show the high degree of protection that vaccinated Ontarians are getting, when taking into consideration that 75 per cent of eligible individuals have received both jabs.

She explained that unvaccinated people make up only one-quarter of the population but 82 per cent of the people in ICU, which shows that “the vaccinated are getting a very high level of protection.”

When asked about breakthrough infections at his weekly news conference on Aug. 24, Ontario’s chief medical officer of health Dr. Kieran Moore had something similar to say. 

“As more and more Ontarians are immunized, over 10 million of us, the unvaccinated are a much smaller number — around 2.2 million that are eligible to be immunized,” he said.

“So when you look at overall infection rates, you’ll see that sometimes a significant number of vaccinated people will get the illness, but they will have less severe symptoms, less risk of hospitalization, less risk of being admitted to the ICU and less risk of death.”

Reggie Lo, professor emeritus in the department of molecular and cellular biology at the University of Guelph, said the recent breakthrough infection rates Ontario has been reporting are quite high, compared to rates that have been previously recorded in several other countries.

For example, an Israeli study from late July by the found a 2.6 per cent COVID-19 breakthrough rate among health-care workers.

As well, Centers for Disease Control and Prevention (CDC) data from reported a 0.01 per cent breakthrough rate in the U.S.

However, this week, showed that 25.3 per cent of people in Los Angeles County who contracted COVID-19 from May to July were fully vaccinated — a rate closer to Ontario’s.

Lo said there are a number of factors that could be contributing to the high breakthrough infection rate in Ontario, such as immune response levels and infection dose.

“One should also look into the severity of illness in these individuals. If they have mild or no symptoms, the vaccination is protecting them,” he added. “The PCR test is amplifying the viral RNA, it could be detecting remnants of the virus, not entire infectious particles, which also mean the vaccination is working.”

He said, however, that the manner in which Ontario has been collecting the data may be creating some inaccuracies. For example, it is possible that the “status unknown” cases reported are from individuals who are unvaccinated but are unwilling to reveal this information.

Regarding third doses, Watts said there is evidence that many seniors in long-term care and people who are immunocompromised have a weaker response to vaccines and for that reason, a third dose is beneficial and should be done as soon as possible.

However, she said, that may not necessarily be the case for all Ontarians in the future.

“I am of the view that we can still wait for the healthy population. There isn’t much evidence yet of declining immunity in this population or whether a third dose would make a difference,” Watts said.

“I think we will be watching the data emerging elsewhere.”