New seroprevalence study of blood donors

By the end of the second wave of the pandemic, 15% of the adult population in Québec had developed antibodies to COVID-19

Montréal, May 27, 2021—A second seroprevalence study of blood donors, conducted by Héma-Québec in collaboration with the Institut national de santé publique (INSPQ) and in partnership with the COVID-19 Immunity Task Force (CITF), estimates that 15% of the adult population in Québec had developed antibodies to the COVID-19 virus by the end of the second wave of the pandemic in March.

These individuals developed antibodies after being infected with the SARS-CoV-2 virus since the start of the pandemic, or after being vaccinated. Excluding those who were vaccinated, results show that almost 10% of the population developed antibodies as a result of infection. These data also confirm that a vast majority of vaccinated people developed antibodies to the virus. This second study was based on a sample of 7,924 individuals aged 18 years or older who made a blood donation between January 25 and March 11, 2021.

It should be noted that a study conducted after the first wave of the pandemic in spring 2020 showed that only 2.2% of individuals tested in the population of blood donors had developed antibodies. After the second wave, at least three times more people were infected. Based on these results, it is possible to extrapolate to almost 600,000 the number of persons between the ages of 20 and 69 who developed antibodies to COVID-19 following an infection since the start of the pandemic. It should also be noted that the first study showed at least half of the infections were asymptomatic.

Differences based on age groups, gender and regions

An analysis of the results shows that seroprevalence rates are higher among young people and decrease progressively based on age. The rates of infection were 19% in those 18 to 24, 16.7% in those 25 to 39, 14.4% in those 40 to 59, 9.8% in those 60 to 69, and 9.5% in those 70 and over.

A significant difference was observed based on gender. The seroprevalence rate was 16.9% in women compared with 12.5% in men.

Not surprisingly, the regions of Laval and Montréal recorded the highest seroprevalence rates, 18.5% and 16.7% respectively. The study also showed that the seroprevalence rate in the Mauricie-Centre-du Québec region was 15.8%, higher than the Québec average. The Chaudière-Appalaches region was close behind with a rate of 15.6%. The other regions posted rates below the Québec average.

Vaccination will be a game changer

One of the important findings of the study confirms that, after the end of the second wave, only a slight proportion of the population had become immunized, a reminder of the importance of pursuing vaccination efforts.

Blood donors: a control group of interest

Blood drive activities in Québec make blood donors a representative group of the general population. Héma-Québec was able to conduct this type of study because the organization already had blood samples for each blood donation and the laboratories and expertise to carry out these tests. Classified as a vital and essential activity, blood drives have continued to be held uninterrupted in most regions of the province since the start of the pandemic. Blood donor samples were collected in 12 of the 18 health regions during the second study.

At the request of the public health authorities, a third similar study of seroprevalence will be conducted in the coming months to monitor the evolution of seroprevalence to COVID-19 in the Québec population.

About Héma-Québec

Héma-Québec’s mission is to efficiently meet the Québec population’s needs for blood and other high-quality biological products of human origin. Héma-Québec has more than 1,500 employees, nearly 255,000 donors of blood, stem cells, breast milk and human tissue, as well as thousands of volunteers at blood drive sites. Héma-Québec delivers nearly 820,000 human-derived biological products to Québec hospitals every year to meet patients’ needs.

Give blood. Give life.

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