Herd immunity to COVID-19 is far from a reality, as only 1.5% of healthy Canadians had been exposed to the virus responsible for the disease in November, according to a new study by Canadian Blood Services and of the Canadian COVID-19 Immunity Working Group (GTIC).
• Read also: All developments in the COVID-19 pandemic
• Read also: COVID-19: economic players in favor of a vaccine passport
These results were obtained by analyzing 33,860 blood donor samples in all provinces except Quebec in November. Even though this rate of 1.5 is modest, it is higher than the 0.88 recorded in October and the 0.70 for the period from May to July.
“Although this is double what was indicated in the preliminary report released after the first wave in May and June, the overall seroprevalence rate, that is, the number of people with antibodies, which suggests a previous infection with COVID-19, remains very low and Canada remains very far from collective immunity, ”said Tim Evans, Executive Director of GTIC.
This study therefore shows that the vast majority of people remain at risk of COVID-19, since they do not have the antibodies to fight the virus.
“Even using serology to add cases to our count that have never been recognized by formal diagnostic tests, it is evident that the vast majority of Canadians remain vulnerable to COVID-19. We have no choice but to maintain public health measures until the immunity acquired by vaccination increases considerably, ”said Dr. Catherine Hankins, co-chair of GTIC.
West in the lead
The proportion of people with antibodies has risen sharply in the west of the country, where the epidemic jumped in the fall compared to the first wave of spring.
“Since the first wave in May and June, seroprevalence in the Prairies (Manitoba and Saskatchewan) has quintupled, from 1.69% to 8.71%. The seroprevalence in British Columbia and Alberta has almost tripled, ”said Dr. Sheila O’Brien, Assistant Director, Epidemiology and Surveillance, Canadian Blood Services.
In contrast, no significant increase was observed in Ontario and the Atlantic in seroprevalence.
The presence of the virus is more frequent in young people aged 17 to 24, whose seroprevalence rate of 2.97% in November was the highest. It is this age group that has also experienced the largest increase since the first wave.
“These findings serve as an important reminder that young adults, although they are less likely to become ill from the infection, should pay attention to public health measures, not only for themselves, but because they are vectors of transmission, ”said Dr David Naylor, co-chair of GTIC.
Whites (1.35%) were also less affected than racialized Canadians (2.5%).