As some Canadian provinces release plans to reopen amid the COVID-19 pandemic, you may have heard people talking about the concept of herd immunity as a key consideration in the design of an offramp from lockdown measures. 

But without answers to questions about who is immune to contracting COVID-19, and for how long, experts say that relying on herd immunity is not a viable option for Canada right now. 

Herd immunity refers to the idea that when enough people in a population become immune to a disease, it can’t effectively spread. In that situation, there aren’t enough uninfected people who can get it and infect others. That widespread immunity can come from a vaccine, or from enough people getting sick that they develop antibodies. But in the case of COVID-19, we don’t have a vaccine — and we don’t know if people who contract the disease once are immune, and if so, for how long. 

“There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” according to the World Health Organization (WHO).  

That’s part of what makes herd immunity a dangerous concept in the absence of an effective vaccine, says Dr. Patrick McDonald, a pediatric neurosurgeon at B.C. Children’s Hospital and faculty member of the University of British Columbia’s National Core for Neuroethics.

WATCH: Prime Minister Justin Trudeau says Canada’s differences precluded clear rules for reopening. Story continues below

If Canada were to target natural herd immunity as a strategic goal, assuming a one-per-cent fatality rate, around 370,000 people could die. If the fatality rate is higher, even more people could die. The Canadian government has increased the COVID-19 fatality rate to 5.5 per cent based on current data, but Dr. Theresa Tam, the country’s chief public health officer, has said it could be as low as one percent.

“Even thinking about herd immunity as a way to deal with it is a relatively dangerous concept,” McDonald told HuffPost Canada. “You might be putting a whole bunch of people at risk, and frankly, [seeing] a whole bunch of people dying, and at the end of the day, there’s actually no benefit to it.”

“I think from a pure ‘how are we ever going to get out of this’ perspective, we’re still very much going to be dependent on the development of an effective vaccine,” he said. 

There are several COVID-19 vaccines under development around the world, but it could be months — or over a year — before one is proven effective, safe, and distributed widely. Some experts estimate a vaccine is 12 to 18 months away.

And with Canada’s economy tanking — the country lost two million jobs in April alone, according to Statistics Canada — some may be tempted to embrace a strategy that will get us on track to our new normal. 

But many experts agree it’s not worth the risks to people’s lives.

Relying on herd immunity isn’t an option at this point for Canada, agreed Alison Thompson, an associate professor at the University of Toronto’s Leslie Dan Faculty of Pharmacy. 

“The only way to really know whether that would work is whether we have the science to say that people are acquiring immunity when they contract the illness, and we just don’t know that at this point,” she told HuffPost.

She said it’s a “risky proposition” to base any reopening strategy on immunity acquired through contracting COVID-19. 

“And it wouldn’t be ethical to rely on that, because it does rely on people getting ill in the first place,” she added.

Quebec toyed with the concept of herd immunity in children as a justification to reopen schools. Horacio Arruda, the province’s public health director, said allowing children to contract COVID-19 and become immunized would help wider society. 

But children who contract the virus, even if they don’t display strong symptoms, can still give it to parents or older relatives.

McDonald points to the United Kingdom, which initially embraced a strategy of letting people go outside to develop herd immunity, but quickly pivoted amid criticism that the strategy would overwhelm hospitals and was already causing more infections and deaths.

Some countries, like Germany, the U.K. and the U.S., have floated the idea of  “immunity passports” for people who have recovered from COVID-19 to go back to work or travel.

The WHO warned against such passports in a briefing note, saying “At this point in the pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an ‘immunity passport’ or ‘risk-free certificate.’”

The organization added that if people assume they are immune to a second infection, they may ignore public health advice, potentially increasing the risk of continued transmission.

At a press conference at the end of April, Prime Minister Justin Trudeau said he doesn’t believe any provinces have a reopening plan that hinges on people being immune to COVID-19.

“The focus we have is on continuing to prevent spread through social distancing measures, through PPE in workplaces, through various measures of protecting Canadians as we move forward,” he said.

He added that Canada’s COVID-19 Immunity Task Force will examine the role that immunity could play in our reopening, but while the science is still unclear, it is important to act cautiously. 

With files from the Canadian Press