HERD IMMUNITY TO COVID-19 MAY NOT BE REACHED IN CANADA FOR A VARIETY OF REASONS, EXPERTS SAY, BUT A RETURN TO LIFE SIMILAR TO THAT BEFORE THE PANDEMIC IS POSSIBLE THROUGH IMMUNIZATION.

Experts predict situation like seasonal flu

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 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.”

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.”