MONTREAL -- Approximately 15 per cent of Quebec adults have developed antibodies to the COVID-19 virus since the end of the second wave in the province.

This is according to the authors of Héma-Québec's second seroprevalence study of blood donors, conducted last March.

The first study, conducted after the first wave in the spring of 2020, showed that barely 2.2 per cent of people in the blood donor group had developed any antibodies.

The Héma-Québec study reports that people developed antibodies either after being infected with SARS-CoV-2 or after being vaccinated.

Approximately 10 per cent of the group developed antibodies as a result of infection.

The data also confirmed that the majority of people vaccinated developed antibodies to the virus.

This second study involved a sample of 7,924 people aged 18 and over who donated blood between January 25 and March 11.

Based on the results, the study estimates the number of people aged 20-69 who have developed antibodies to COVID-19 as a result of infection since the start of the pandemic to be almost 600,000.

The authors note one important finding is that by the end of the second wave, only a small part of the population was immune. They emphasize the importance of continuing vaccination efforts throughout the province.

Analysis of the results shows that seroprevalence, the percentage of individuals who have antibodies to an infectious agent, are higher among young people and decrease progressively with age: 19 per cent for 18 to 24-year-olds, 16.7 per cent for 25 to 39-year-olds, 14.4 per cent for 40 to 59-year-olds, 9.8 per cent for 60 to 69-year-olds and 9.5 per cent for those 70 and over.

It is 16.9 per cent among women, while it is 12.5 per cent among men.

The highest rates were found in the Laval and Montreal regions, at 18.5 per cent and 16.7 per cent.

The study also shows the rate in Mauricie-Centre-du-Québec is 15.8 per cent, higher than the Quebec average. The Chaudière-Appalaches region followed closely at 15.6 per cent.

Most of the other regions measured below the Quebec average.

A third study will be conducted in the coming months, at the request of public health authorities, to continue monitoring the evolution of COVID-19 seroprevalence in the population.

The Héma-Québec studies are being conducted in collaboration with the Institut national de santé publique (INSPQ) and in partnership with the Groupe de travail sur l'immunité face à la COVID-19 (GTIC).

-- This report by The Canadian Press was first published in French on May 27, 2021.