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Canada may find it challenging to reach herd immunity from COVID-19, experts say

Last Updated May 6, 2021 at 6:35 am PDT

Pfizer-BioNTech COVID-19 vaccine at the Strathcona Paper Centre in Napanee, Ontario, on Monday March 15, 2021. THE CANADIAN PRESS/Lars Hagberg
Summary

There are suggestions we may always be living with COVID-19 because of the difficulties in achieving true herd immunity

Experts say return to life a lot like it was before the pandemic is possible through immunization

New poll finds many Canadians don't envision life getting back to normal until 2022 or later

Herd immunity may not be reached in Canada but a return to life similar to that before COVID-19 is possible through immunization, experts say.

Such immunity is achieved when enough people are immune to a virus, either through vaccinations or natural infections or a combination of both.

Prof. Paul Tupper of Simon Fraser University’s mathematics department said herd immunity is unlikely to happen with COVID-19 for a few reasons.

The virus is being transmitted worldwide, which means it is reintroduced in different places across borders and immunity through vaccination and infection doesn’t last permanently. The vaccines don’t seem to be completely effective against some of the new variants, he said.

“So, I think what is more likely to happen is that we end up in a situation like we have with seasonal flu,” Tupper said.

“We have to live with the flu, and I think something similar is going to happen with COVID.”

The challenges created by variants

The level of immunity among the population also changes with the variants, especially the more transmissible strains, he said.

Sarah Otto, a University of British Columbia professor, said the disease’s reproductive rate is hard to pinpoint, which makes it difficult to establish a herd immunity target. Otto is an expert on the mathematical models of pandemic growth and control in the university’s zoology department.

The reproductive rate is the number of additional people infected by a single person with COVID-19, which has also changed because of the variants, she said.

Canada might also fall short of herd immunity because people can still get infected after vaccination, even if they are less likely to develop symptoms, she said.

“We don’t yet know how effective vaccines are at reducing transmission from person to person and that matters a lot,” Otto said.

Vaccinated people are getting fewer infections but those who do can still suffer severe symptoms, she said

“Before the pandemic, we didn’t have working vaccines for coronaviruses, so we don’t know exactly what the outcomes are going to be. It’s very unusual to have a disease with such wildly differing outcomes, with asymptomatic individuals and severely affected long haulers. How are vaccines going to change that mix? We don’t really know why the severe cases are so severe.”

Vaccines reducing transmission rates

Tupper said public health guidelines will change as more people get vaccinated.

“But the goal of eradicating COVID just does not appear to be realistic.”

Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto, said vaccines can significantly reduce transmission rates, regardless of whether Canada reaches herd immunity.

“Some communities might have no transmission while other communities, even within the same province, might have some low levels of transmission and it’s all based on vaccine status,” he said.

“But regardless, we will achieve very, very low rates of transmission in our communities because of vaccination.”


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Community level immunity is when a virus is not completely eliminated, he said.

“There may be some transmission of COVID-19 but sporadically with small outbreaks or with low levels of transmission, while most people are largely unaffected due to widespread vaccination.”

It had been suggested that herd immunity could be reached when about 70 per cent of the population is vaccinated, but now researchers don’t know what level of protection is required because of the variants.

Otto said there are more questions than answers at this point.

“With every partial answer we get two or three more questions. These are hard and tricky issues and I wish we were less uncertain, but that is the truth of the matter.”

How Canadians are feeling

As we navigate the headlines, a new poll from Maru has found an increasing number of Canadians — two thirds — believe the pandemic will get worse before it gets better.

That’s a 20 per cent jump since March.

Canadians are also feeling more negative than positive, with 57 per cent of respondents saying they have negative feelings.

Close to 40 per cent of survey takers say they’re feeling frustrated or anxious, but there are many who say they’re feeling fortunate.

Isolation and boredom were also themes that came out of Maru’s survey.

However, there were some positives. About one in three Canadians say they’re feeling optimistic, with “calm” an emotion following close behind.

When it comes to when exactly life will get back to “normal,” respondents largely say they don’t envision that return until 2022 or even later.

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