White Coat, Black Art·The Dose

Focus on vaccination rates, not herd immunity as the way out of the pandemic: expert

Catherine Hankins, the co-chair of Canada’s COVID-19 Immunity Task Force, explains why achieving herd immunity may be elusive, but stopping transmission with vaccines can lead to a similar return to some semblance of normalcy — and that should be the focus.

Data coming soon on mixing & matching vaccines could help

New Zealand band Six60 performs in Auckland, New Zealand, April 24, in front of 50,000 people. While there are questions around whether Canada can achieve herd immunity, experts say high vaccination rates can allow Canadians to return to some semblance of normal where big concerts may be possible again. (AP Photo/David Rowland)

If you have been seeing headlines that say herd immunity to COVID-19 isn't going to happen, Dr. Catherine Hankins has a message for you: "Don't panic."

Instead, focus on getting vaccinated as soon as you can, with the first vaccine offered to you, said Hankins, co-chair of Canada's COVID-19 Immunity Task Force.

"People are hiding behind believing that if we can just get to herd immunity, it's going to be all over,'" Hankins, a professor of public and population health at McGill University, told Dr. Brian Goldman, host of The Dose and White Coat, Black Art

But while herd immunity may be elusive, stopping transmission with vaccines can restore a similar semblance of normalcy, she said. 

Catherine Hankins, the co-chair of Canada’s COVID-19 Immunity Task Force, says factors like the coronavirus variants-of-concerns may mean Canada doesn't achieve herd immunity any time soon — or at all. (Submitted by Catherine Hankins )

Herd immunity occurs when enough of a population is immune to a virus — either naturally from infection or through vaccination — so the virus can't find hosts and eventually dies off.

The threshold for herd immunity is different depending on the virus. For COVID-19, people initially thought we'd need about 60-70 per cent of the population to be immune in order to achieve it, said Hankins

Now she said that threshold is thought to be much higher — and possibly unattainable — because of a number of variables:

  • Variants of concern: Some of the variants have upwards of 60 per cent higher rates of transmission. That's prompted experts to adjust their targets for herd immunity as high as 80 per cent. 

  • Waning immunity: Studies have found that antibodies eventually decline in people who have recovered from COVID-19. Scientists are also studying what's known as breakthrough infections where people fall sick with COVID  despite being vaccinated, or get COVID a second time.

  • Kids and teens: Health Canada just approved an application from Pfizer-BioNTech  to use its vaccine in children as young as 12. (Previously it had only been approved for those 16 and up.) Still, that leaves 4.8 million kids — or 13 per cent of the population — ineligible for any vaccine. 

In this March 24 image provided by Duke Health, Alejandra Gerardo, 9, looks up to her mom, Dr. Susanna Naggie, as she gets the first of two Pfizer COVID-19 vaccinations during a clinical trial for children at Duke Health in Durham, N.C. (Shawn Rocco/Duke Health/Associated Press)

Vaccines cut transmission

Whatever the mechanism, reducing transmission is key to returning to a world where we can go to concerts and hug loved ones, said Hankins, and there's increasingly "good news" about vaccines and transmission.

Hankins pointed to a new study out of the U.K., by Public Health England, which showed that one dose of the COVID-19 vaccine reduces household transmission by up to half. 

It found that even those unfortunate enough to become infected three weeks after receiving one dose of the Pfizer-BioNTech or AstraZeneca were between 38 and 49 per cent less likely to pass the virus on to their household contacts than those who were unvaccinated. 

Carolyn Ellis, left, creator of the hug glove, hugs her mother Susan Watts, 74, in her backyard on Christmas Eve during the COVID-19 pandemic in Guelph, Ont., in December 2020. The key to a return to real hugs, with no plastic in between, is focusing on vaccination rates, not herd immunity, experts say. (THE CANADIAN PRESS/Nathan Denette)

On Monday, the vice-chair of Canada's National Advisory Committee on Immunization said that mRNA vaccines like Pfizer-BioNTech and Moderna are "preferred" because of the small risk of serious blood clots from the AstraZeneca and one-dose Johnson & Johnson vaccines. 

This came after months of official messaging to take the first vaccine offered to you — advice Hankins stands by.

"So this [U.K. study] tells us, get your first dose, whatever it is, get it in you, because it's going to protect you from severe disease and from infection. And it's going to … reduce your risk of transferring the virus to somebody that you live with."

WATCH | Pfizer, Moderna vaccines preferred type, NACI says:

Vaccine advisory group says Pfizer and Moderna COVID vaccines are the preferred type

1 month ago
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Dr. Shelley Deeks of NACI discussed with reporters the merits of receiving one type of COVID-19 vaccine over another. 2:32

Mixing and Matching vaccines

Aside from the one-dose Johnson & Johnson vaccine, the current guidance is to receive a second dose of the same vaccine you were first vaccinated with. But that could soon change. 

With varying supplies of different vaccines, mixing and matching would mean some flexibility, allowing people to get their second doses faster, rather than waiting for supply of one particular brand to be available.

On Tuesday, Dr. Theresa Tam, Canada's top doctor, said Health Canada is "very closely" watching data around the mixing and matching of COVID-19 vaccines.

A trial led by Oxford University in the United Kingdom is testing the safety and efficacy of mixing different shots.

The study includes adults over 50 who had a first dose of Pfizer or AstraZeneca. Their second dose could be the same again, or a shot of Moderna and Novavax. Results of this first stage are expected sometime this month or next.

People line up outside an immunization clinic to get their Oxford-AstraZeneca COVID-19 vaccine in Edmonton, April 20. (Jason Franson/The Canadian Press)

Tania Watts, a professor of immunology at the University of Toronto, said that mixing and matching might actually improve your immunity. 

"From my point of view as an immunologist, on a theoretical basis, I think it's probably going to be perfectly fine and it even potentially could be better to have a boost with a different one."

Regardless of whether mixing and matching happens, Watts finds optimism in Canadians' enthusiasm for getting vaccinated. 

"I think Canada has a good chance of having COVID-19 highly controlled, but perhaps not 100 per cent eliminated."

A man stops to look at the menu of the one takeaway restaurant open at an empty shopping complex in Vancouver's Chinatown on April 25. Experts say lifting public health restrictions should happen gradually as more and more people are vaccinated. (THE CANADIAN PRESS/Darryl Dyck)

Hankins agreed but warned there won't be one big moment where everything returns to normal all at once.

"It's not like we're going to reach some kind of herd immunity threshold and now everything's going to be fine. We're going to be living with this for many years to come."

"We've got to figure out how to do it in a way that … allows us to open up and have as much as we want of the kind of life we had before, but as safely as possible," Hankins added.


Written and produced by Willow Smith.

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