Canada's top doctor says too little is known to consider using a newly approved serology test to identify individuals who could be immune to COVID-19 and allow those people to return to work or gather in public.
Instead, Theresa Tam said Wednesday that the new LIAISON test will be used more broadly to look for immunity in the Canadian population, noting questions persist about the prevalence of COVID-19 antibodies and what protections they offer.
Tam said an immunity task force had been formed to examine what protection from reinfection exists among those who have recovered from COVID-19.
"Now that you have the first test, we're hoping to see rapid implementation of the actual population surveys, both general and those focusing on specific communities, geographies, (and) occupational groups," said Tam, Canada's chief public health officer.
"They're working as fast as they can and hopefully this will be quite rapid in terms of its rollout."
The comments came a day after Health Canada said it had authorized the first serological test to detect antibodies specific to the virus that causes COVID-19.
The federal agency said Tuesday that at least one million Canadian blood samples will be collected and tested over the next two years to track the virus in the general population and in specific groups at greater risk of having been infected, including health-care workers and seniors.
Even if a test has been authorized, Tam said Health Canada must monitor its ability to perform in real-life applications.
"How specific are they? Can they actually detect the specific COVID-19 antibodies or not?" said Tam.
"All of that remains to be seen which just means that we need to evaluate and monitor these tests as carefully as we can."
Unlike the current PCR diagnostic tests that tell us where COVID-19 is presently, serology tests reveal if someone has been infected in the past and has developed antibodies to the virus.
Experts say that can give us a better sense of how prevalent infection has been and how to further prevent COVID-19 spread — information that is critical as various regions of the country begin to reopen.
Nova Scotia's chief medical officer of health noted Wednesday that serology tests could provide good information on the role asymptomatic people play in community spread.
"Nationally, there is discussion about doing a sero-survey. So you do a sample of people across the country, big enough that you can get representative numbers from each of the provinces and territories. Through that, you get a sense of how many people have been actually immune from wave one, and then we could match that up with a number of known cases we have," said Dr. Robert Strang.
"And the difference would give us an estimation of the number of people that weren't recognized — either they were asymptomatic or never came forward for testing."
At the other end of the country, B.C.'s provincial health officer has already invited residents there to volunteer for a serology blood testing study.
Dr. Bonnie Henry announced the study Tuesday, along with a survey to gather information about how people have been affected by COVID-19 measures.
Patrick Saunders-Hastings, an epidemiologist and consultant with the management consulting firm Gevity Consulting Inc., said one issue with serological tests in general has been their reliability.
He agreed that the goal should be to try to determine on a broad scale who has antibodies that may protect them from the coronavirus rather than aim for individual immunity passports.
"Serological testing performance is quite variable," said Saunders-Hastings, director of life sciences and environmental health at the firm.
"And when we do get down to the individual levels some of the sort of false positives and false negatives can be quite problematic."
He added that serology should be used as a complement to ongoing clinical diagnostic testing, which would identify current infections.
Also unknown: the amount of antibodies needed to confer full immunity and how long immunity lasts.
Tam said it was too early to discuss the possibility of so-called immunity passports, which the World Health Organization has cautioned against.
"We really we need more information."
This report by The Canadian Press was first published May 13, 2020
Cassandra Szklarski, The Canadian Press