The approximately 34,000 samples that were analyzed came from Canadians from all provinces except Quebec, and none came from the territories. The presence of antibodies in the samples suggests a previous infection with COVID-19.
According to Dr. Catherine Hankins, co-chair of the COVID-19 Immunity Working Group, the study provides a snapshot of the prevalence of the virus among blood donors, that is, healthy Canadians. people who live in cities and between the ages of 17 and 65.
It’s a photo, but it’s not representative of the general population
, she notes, qualifying this study as piece of the puzzle
the actual number of Canadians who have been infected with COVID-19.
It is likely that the people we see here in the numbers are people who were asymptomatic, and it really reflects community transmission.
, explains Dr. Hankins.
It is important to limit community transmission, among other things, since this can lead to new variants of the virus, she adds.
Dr. Hankins says the most important message from this study is that despite the fact that the rate has doubled since May and June
, it remains very very low. This means that the vast, ultra-large majority of Canadians are still susceptible to this infection.
.
Thus, the study concludes that health authorities should maintain restrictions until vaccination achieves herd immunity.
Higher seroprevalence among young people and people of color
Donors aged 17 to 24 had the highest seroprevalence rates of 2.97% in November, and experienced the largest increase since the first wave, compared to other age groups.
These are people who were probably asymptomatic, who didn’t know they had the virus. It is very important that they protect themselves and that they protect others around them
, says Dr. Hankins.
The study also shows that Canadians of color continue to have higher HIV prevalence rates (2.5%) than those of donors who identify as white (1.35%).
According to Dr. Hankins, this is because people of color are more likely to be exposed to the virus. She notes that they are overrepresented in employment sectors where the virus is spread, such as long-term care homes, hospitals and jobs where they must interact directly with the public.
Seroprevalence explosion in the Prairies
We saw, during the first wave, that the Prairies were not much affected, the rates were below the Canadian average
, recalls Dr. Hankins.
But the province that has experienced the greatest increase in the seroprevalence rate, and therefore where donors have developed the most antibodies, is Manitoba. From May to July, only 0.6% of blood donors had antibodies against the virus.
In October, this figure reached 2.96%, and in November 8.56%. The second highest rate was 4.17% in Saskatchewan. Alberta is ranked third with 1.79%.
Dr Hankins suspects the study captured the extent of community transmission in Manitoba, when that province was struggling with the highest number of active cases in the country.
Manitoba had [le nombre de cas] the highest per capita, so I think we captured a little what was happening in November among Manitobans
, she argues.
The study shows that the seroprevalence in British Columbia and Alberta has almost tripled since the first wave.
No increase in Ontario
Conversely, no significant increase in seroprevalence in blood donors was observed in Ontario and the Maritimes. This finding surprises Catherine Hankins, given that the number of cases was relatively high in Ontario.
What surprises me a little is Ontario, because in the end things haven’t changed, neither the province, nor Toronto and Ottawa. We had to look into it to try to understand
, she says.
Dr. Hankins suspects highly localized outbreaks in populations less represented among blood donors. She gives the example of nursing homes or certain disadvantaged neighborhoods.
In addition, with the start of vaccination against COVID-19 in Canada, Canadian Blood Services is looking into the use of a test that allows samples to be analyzed in order to distinguish immunity acquired by infection from immunity acquired by a vaccine.
