As of April 8, 2021, more than seven million doses of the COVID-19 vaccine have been administered in Canada, and approximately 17 per cent of the population has received at least one dose.
While the majority of Canadians are still waiting for their dose, only 12 per cent of Canadians said they did not intend to get vaccinated, according to a recent Leger survey. To reach herd immunity, when a significant portion of the population becomes immune to infection through vaccination or natural infection, 53 to 84 per cent of Canadians would need immunity, taking into account the strongest variants and the speed at which one could spread.
How long immunization will last, and whether Canadians will need shots annually against COVID-19 is unresolved.
Several factors will determine immune response to a vaccine — including age, sex, genetics, comorbidities, behaviour, nutrition and environment — so it can vary from person to person.
Still, clinical trials, and now real-world data, show vaccines from Pfizer-BioNTech and Moderna to be at least 90 per cent effective following two or more weeks of vaccinations of the recommended doses.
COVID-19 variants 'definitely a concern'
Yanet Valdez Tejeira, a Vancouver-based immunologist, infectious disease expert, and volunteer lead at COVID-19 Resources Canada says researchers are currently extrapolating data from clinical trials that started last year to see how long immunization from COVID-19 vaccines will last.
"I know for sure that at least one vaccine, Pfizer-BioNTech, confirmed on April 1 that its vaccine offers protection lasting at least six months after the second dose," Tejeira said.
She is hopeful that researchers will follow participants for years to evaluate the long-term effects and effectiveness of the vaccines, but current data suggests immunity could last beyond the guaranteed time of six months.
Health Canada says exact duration of immunity from the vaccine is unknown and researchers are still looking at the data as it is coming in.
"We will continue to work with partners to monitor the evidence on the long-term effectiveness of our authorized vaccines, and how they protect against variants of concern," said Health Canada and Public Health Agency of Canada spokesperson Anna Maddison.
Although the vaccines have been effective in preventing severe disease, hospitalization and death from the original strain of the virus, studies are only now starting to account for the vaccine's effectiveness against variants of COVID-19.
"The effectiveness of vaccines against emerging variants is definitely a concern, and depends on the type of vaccine," Tejeira said. "The Pfizer one, for example, appeared to be fully effective against the worrisome B.1.351 variant [from South Africa] of the virus. On the other hand, AstraZeneca’s vaccine appears to be less effective against this same variant."
Researchers are worried if more people keep getting infected, more variants will emerge against which the vaccines may not be able to protect.
Does a stronger immune response to the vaccine mean longer immunity duration?
An effective immune response from a vaccine means the body is protected from a virus without hurting its own cells by inducing inflammatory response and killing the virus.
"A strong antibody response does not mean that the body is better able to neutralize the pathogen," Tejeira said.
"COVID-19 in particular is dangerous because a high percentage of patients develop autoantibodies, which are primed to respond to your own molecules and not the pathogen."
Tejeira added: "A key aspect of immunity is memory. We want our B cells to remember the pathogen it fought, so they will activate pathogen-specific antibodies when they encounter it again."
Will we need booster shots? Does this mean Canada will have to secure 30M doses every six months?
The Immunity spectrum varies depending on the virus. A vaccine for measles offers protection for life whereas a vaccine for influenza is seasonal and lasts a few months.
While there are no booster shots available yet or even vaccines created for certain variants, development is underway and researchers will start trials once they are ready.
Tejeira says Canada should secure booster shots given the circumstances, as more variants arise with no sign of herd immunity any time soon.
"If COVID-19 and its variants are still widely present, vaccine protection wanes within the year, and population immunity has not yet been reached, then Canada should secure and distribute booster shots," Tejeira said.
Pfizer says based on their research and real world evidence, they have not seen changes to antibody levels that could reduce protection from their vaccine doses. But Canada is monitoring the progress of the other vaccine candidates under contract that are still at the development stage and planning to get booster shots.
"Canada is in discussions with vaccine developers regarding plans for early and secure access to booster and variant vaccines when they become available." Maddison said.
If immunization runs out within the year, Canada may need to secure booster shots especially if more variants emerge, but as research is coming in and people are being vaccinated, we will know better with time.
While the vaccine rollout has been slow, experts like Tejeira are hoping the federal government can accelerate the process of setting up infrastructure for vaccine production in Canada so the country does not have to rely on foreign vaccine production.
"We should continue to focus our efforts on vaccinating everyone. This will give us a better chance at reducing infections, and thus the risk of generating new variants our existing vaccines can’t guard us against," Tejeira added.
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