Blood tests for coronavirus antibodies reveal ‘undetected infections’ in Canada

TORONTO — Testing of recently donated blood reveals little evidence of widespread infection by the novel coronavirus, scientists said Thursday.

Canadian Blood Services and Canada’s COVID-19 Immunity Task Force revealed that less than one per cent of the 10,000 samples tested thus far have come up positive for SARS-CoV-2 antibodies, which are present in anyone who has fought off the virus.

Although the percentage is small, it is still concerning because it suggests there are “several undetected infections” for every confirmed Canadian case of COVID-19, task force co-chair Dr. David Naylor said in a press release. More than 112,000 Canadian cases had been confirmed as of Thursday morning, representing about 0.3 per cent of the total population.

The fact that more than 99 per cent of donated blood samples contained no antibodies protecting against SARS-CoV-2 should also serve as a warning for most Canadians as the country reopens, force co-chair Dr. Catherine Haskins said in the release.

“By far, the majority of us remain vulnerable to infection,” she said.

“We need to ramp up testing and tracing capacity across the country to interrupt any chains of transmission quickly to prevent unchecked spread.”

All of the tested samples were donated between May 9 and June 8, just after virus activity peaked in Canada. The batch does not include any samples from Quebec, which has been the hardest-hit province. Results from Quebec are expected to be made public “in the near future,” according to the press release from the task force.

Further country-wide data is also coming, as Canadian Blood Services is working on testing all 37,800 blood samples donated during May and June.

It is not yet clear how long antibodies that are generated to help the body battle SARS-CoV-2 infection last. Research published this week in the New England Journal of Medicine suggests that half of the antibodies disappear within 36 days.


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