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Coronavirus: What is herd immunity and what does it mean for COVID-19?

Coronavirus outbreak: Trudeau says they may look at loosening virus-control measures in summer
WATCH: Trudeau says they may look at loosening virus-control measures in summer

As the novel coronavirus continues to spread in Canada and around the globe, the concept of herd immunity has been put into the spotlight.

In Canada, officials have shuttered schools and all non-essential businesses, have limited all non-essential travel and have urged the public to practice physical distancing in order to stem the spread of COVID-19 and give researchers time to develop a vaccine.

The science of vaccines
The science of vaccines

But, if scientists aren’t successful in creating a vaccine, the country would need to develop what is known as natural herd immunity in order for the pandemic to end.

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What is herd immunity and what does it mean for COVID-19? Here’s what experts say.

What is herd immunity?

“The idea of herd immunity is that you have enough people in the population who are immune [to a virus] and you’re either immune because you had the infection already, or you’ve been vaccinated,” Dr. Jeff Kwong, an infectious disease specialist and associate professor in the department of family and community medicine at the University of Toronto said.
Coronavirus outbreak: Trudeau says Canada has tested ‘significantly more’ people in total than U.S.
Coronavirus outbreak: Trudeau says Canada has tested ‘significantly more’ people in total than U.S.

Kwong said if you have enough people who are immune in the population, then the infection won’t spread as easily.

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“Or ideally it won’t spread at all,” he said.

Dr. Suzanne Sicchia, an associate professor at the Interdisciplinary Centre for Health and Society at the University of Toronto Scarborough said the larger the proportion of people in the population who have natural or vaccine-based immunity to a given infectious disease, the fewer people there are that the micro-organism or disease-causing agent could infect.

Coronavirus around the world: April 11, 2020
Coronavirus around the world: April 11, 2020

“In this way, herd immunity can help to eliminate the infectious agent in a particular population,” she wrote in an email to Global News.

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However, Sicchia noted that elimination is not the same as eradication.

“Elimination can be for a period of time whereas eradication refers to complete elimination of a disease in a region or globally.”

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READ MORE: Live updates — Coronavirus in Canada

According to Sicchia, Canada has developed herd immunity against other viruses.

“Herd immunity happens whenever a BIG chunk of the population has been vaccinated for example,” she wrote. “And of course we have eradicated both Smallpox and Polio!”

Herd immunity and COVID-19

Since the novel coronavirus outbreak began, researchers have been working tirelessly to develop a vaccine in order to prevent the spread of COVID-19.

It is estimated it will be made available for use sometime in the next two years.

However, if researchers are unable to successfully develop a vaccine, Kwong said Canada would need to develop herd immunity in order for the pandemic to end.

Coronavirus outbreak: Trudeau warns Canadians to expect ‘wavelets’ of COVID-19 outbreaks in coming months
Coronavirus outbreak: Trudeau warns Canadians to expect ‘wavelets’ of COVID-19 outbreaks in coming months

He said in order for that to happen, around half of the country’s population would need to develop immunity.

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“So operating on the assumption that they do have protection after you’ve had the virus once, it’s probably going to be more than 50 per cent,” he said.

But, Kwong said researchers are not sure how long the immunity lasts.

“I’m not sure anyone knows,” he said. “I think especially because this is a new virus, we don’t know.”

READ MORE: Ontario reports 411 new coronavirus cases, 31 deaths as total cases top 6,600

Another unknown, Kwong said, is how many people in Canada may already have developed immunity to the virus.

He said researchers are already hard at work trying to determine exactly what percentage of the population has already had the infection and would be considered protected from COVID-19.

However, it is possible, Kwong said, that even those who have had the virus may not be immune.

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Coronavirus outbreak: Canada’s top doctor says death toll has hit 600
We’re hoping that if you’ve had the virus then you are considered immune, [but] it’s possible that they’re not,” he said.
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“But we don’t know — we just don’t know right now.

A ‘serious mis-step’

Some countries — including the U.K. — have considered not implementing these types of measures, and have instead looked into allowing the virus to spread widely, to develop herd immunity.

Sicchia said this strategy is “completely wrong-headed and dangerous.”

READ MORE: Britain’s Boris Johnson making ‘very good progress’ in COVID-19 recovery, official says

“To be frank, when [Boris] Johnson went on BBC Newsnight and called for a ‘nice big epidemic’ that they thought could somehow ‘control’ I was appalled — doing so would have meant a great many deaths!”

Kwong, too, called the idea “dangerous.”

“The whole idea of flattening the curve is that you don’t allow too many people to get very sick at the same time.”

He said if more people are sick than the health system can handle, then a “lot of people die.”

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Coronavirus outbreak: Trudeau says end of COVID-19 ‘first wave’ likely to come in the summer

Sicchia said “thankfully” the U.K. recognized this was a “serious mis-step and changed their course.”

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According to Sicchia, physical distancing along with other public health measures including widespread testing, social isolation after travel, and practising good hand and respiratory hygiene, paired with bolstering the health care sector, is the most effective route to ending the pandemic.

READ MORE: Reality check — Would Albert benefit by letting COVID-19 spread among young people to build up herd immunity?

On Friday, the Canadian government released models which suggested the first wave of the virus could end this summer.

Prime Minister Justin Trudeau said based on these projections, some measures may be able to be loosened in the summer, but said Canada will not be able to return to the normal “we had before” until a vaccine is developed.

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Coronavirus outbreak: Tam says projections show Canadians must ‘double-down’ on prevention measures

According to the Public Health Agency of Canada, as of Saturday at 11 a.m. ET, there were 22,595 confirmed cases of COVID-19 in Canada.

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So far, COVID-19 has claimed 600 lives across the country.