Although Canada has secured four contracts for more 190 million doses of potential COVID-19 vaccines, health officials aren’t sure how many people will need to receive it.
Deputy public health officer Dr. Howard Njoo said Tuesday (Sept. 1) that the level of vaccination to achieve community, or herd, protection varies by the disease.
“That’s still to be determined because the science is not clear on that yet,” Njoo said.
“For a very contagious disease like measles the vaccine uptake needs to be much higher to determine that level of community protection. We don’t know that yet for COVID-19.”
There are currently at least 128,948 total test positive cases of the virus in Canada, with more than 9,100 deaths.
For measles, the Canadian government has a goal of 95 per cent vaccination by 2025. According to John Hopkins University, early estimates of the virus’s infectiousness point to at least 60 to 70 per cent of the population needing to be vaccinated to achieve herd protection. A recent poll suggests that about 14 per cent of Canadians will not get the vaccine altogether, while nearly one-third will adopt a “wait and see” approach.
It’s also unclear how effective an eventual vaccine will be.
“International consensus is that we should at least look at vaccines that are around the 50 per cent vaccine efficacy mark,” chief public health officer Dr. Theresa Tam said, echoing similar statements from other public health researchers.
“This means that an individual who was vaccinated would be 50 per cent less likely to get COVID disease—or whatever the particular endpoint is that’s measured in the trial—than individuals that weren’t vaccinated,” said Dr. Ruth Karron, who leads the Center for Immunization Research at the Johns Hopkins Bloomberg School of Public Health.
But Canadian health officials were sure on one point; going for a herd immunity approach by letting the disease run through the population was not effective. Tam called it an “extremely difficult strategy” because of the potential for exponential growth that could overwhelm health-care systems.
“What we do know that even in the most [COVID-19] affected parts of the world, the level of population immunity seems quite low, so getting high enough vaccine uptake is going to be quite important,” Tam said.
Currently, Canada has agreements with Johnson & Johnson, Novavax, Pfizer and Moderna, if any of the four companies develop an effective vaccine. Any vaccine will have to be approved by Health Canada before Canadians can get it.
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