A study by Canadian Blood Services and the COVID-19 Immunity Task Force has shown that a low number of Canadians may have antibodies to the coronavirus.
The seroprevalence study, conducted between May 9 and June 18, identified antibodies in the blood, as they are an indicator of past infection and can generally be detected close to the onset of an infection.
Based on an analysis of 37,373 blood samples from across the country, the results suggest that as few as 0.7 per cent of healthy Canadians have been exposed to SARS-CoV-2, the virus causing COVID-19.
“Antibody levels do decline rapidly and may have disappeared in some people by the time of testing. Second, blood donors, in general, are health-conscious and healthier than the general population,” said task force co-chair Catherine Hawkins, explaining why the percentage may be lower than anticipated.
“Nonetheless, these results once again tell us how few Canadians were infected by SARS-CoV-2 by the end of May. This shows that when all actors, especially individual citizens, follow good public health practices, the risk of infection diminishes considerably.”
Alberta’s seroprevalence, or percentage of the population that appears to have been infected, was 0.37 per cent, among the lowest in the country. Calgary was at 0.43 per cent of positive tests, while Edmonton sat at 0.38.
The authors of the study cautioned that the numbers aren’t quite cause for celebration.
“Global data suggest that population-wide infection rates estimated from SARS-CoV-2 antibodies are about 50 per cent higher than those measured in blood donor samples.
“But even if we doubled or tripled the estimates from this study, there is little to no likelihood that levels of immunity in the population are high enough to slow down a second wave of COVID-19 infection,” says task force co-chair David Naylor.
“As such, it’s critical to ramp-up testing and tracing capacity across the country to reduce risk in settings, such as workplaces and schools, and to interrupt any chains of transmission quickly to prevent spread.”