Is herd immunity still possible in Canada? Experts aren't so sure
TORONTO -- With new cases of COVID-19 variants being confirmed across Canada, some experts say achieving herd immunity is no longer possible, or may require a much higher percentage of the population being vaccinated than previously thought.
Experts say herd immunity is achieved when most of a country’s population -- estimates vary from 60 to 80 per cent -- have acquired defences against a virus, whether through vaccination or because they caught the disease and survived.
The specific percentage threshold hasn’t been settled on in Canada, but Health Canada's chief medical adviser Dr. Supriya Sharma previously told the House of Commons health committee that vaccination rates will likely have to be even higher than the popular estimates to ensure those who cannot get vaccinated are protected.
"Now with the emergence of variants and because they are more transmissible, I think a lot of people are adjusting those numbers up towards more like 85 per cent, or even potentially 90 per cent coverage to achieve herd immunity," Sharma said.
"Certainly it's a moving target, because as we know, the virus and its transmissibility and how contagious it is, is changing," she added.
Jeff Kwong, an epidemiologist with the Sunnybrook Research Institute in Toronto, told CTVNews.ca on Thursday that reaching herd immunity in Canada is still possible, but "what level of immunity needed to achieve that is uncertain."
"With the new variants being more transmissible, we will likely need higher levels of immunity in the population to have herd immunity," Kwong said in an email.
He estimates that the immunity threshold would likely be somewhere around 80 per cent of the population being vaccinated.
MORE TO CONSIDER THAN VACCINATION RATES
Canada has reached herd immunity before against other diseases, such as the measles. However, experts aren't so sure the same will happen with the novel coronavirus.
Eleanor Fish, a senior immunologist with the Toronto-based University Health Network, says there are a variety factors impacting herd immunity beyond just vaccination rates, including asymptomatic transmission, the extended time between vaccine doses, and the level of protection Canadians previously infected with COVID-19 have against new variants.
"So guestimating herd immunity with all these moving parts -- it's nigh on impossible from my perspective," Fish said in an email.
Dr. Anna Banerji, an infectious disease expert and the director of global and Indigenous health at the University of Toronto, says achieving herd immunity is no longer possible because Canada isn' vaccinating all of its residents
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She explained in a telephone interview on Thursday that Canada is not currently vaccinating children, leaving out a major portion of the entire population.
"To have herd immunity, you have to have a large percentage of the population vaccinated, and that includes the whole population -- anyone susceptible to COVID -- so that includes children," Banerji said.
"As long as you have children not vaccinated, the virus can go to children, it can spread through them, they can act as a reservoir to come back and infect people," she added.
While herd immunity may still seem like an achievable goal to some, Banerji said the focus should be on vaccinating as many Canadians as possible.
"Whoever gets the vaccine has a much, much reduced risk of getting COVID, but also a greatly reduced risk of getting severely sick from COVID, ending up in the hospital and dying from it. For each individual that gets vaccinated, that reduces the risk of them getting it, but also the people around them," Banerji said.
She added that ramping up vaccinations will also subsequently limit the spread of more contagious variants.
"If there are a lot of people with COVID and a lot of virus out there, then it's more likely that the virus is going to mutate, but if people are mostly vaccinated, then it slows down the mutation," Banerji explained.
WHAT HAPPENS IF HERD IMMUNITY IS ACHIEVED?
Even if herd immunity is achieved, Deputy Chief Public Health Officer Dr. Howard Njoo has said that the easing of public health restrictions won't immediately happen.
He said returning to normal will depend on more than the percentage of people who are vaccinated, including the number of hospitalizations and the number of variant cases across the country.
"At this point, no one knows how many people need to be vaccinated, you know, what might be the sufficient level of vaccine coverage to get herd immunity, so that's why I think we can't just rely on vaccination," Njoo said.
Public health officials have signalled that even when vaccines become widespread, there will need to be precautionary measures like frequent hand-washing, physical distancing and mask-wearing in place for some time.
"I don't think we'll ever get back to what normal was, you know, pre-COVID, I think it'd be a different kind of what normal is," said Njoo.
With a file from CTVNews.ca's Rachel Aiello