Antibody tests could guide easing of social distancing
First priority is letting health-care workers know if they are immune
When restrictions on our personal and working lives are lifted will depend on some complicated math and the level of herd immunity to COVID-19 that develops among British Columbians.
Somewhere between 30 and 70 per cent could eventually be infected with a novel coronavirus as transmissible as the one that causes COVID -19, according to Dr. Mel Krajden, medical director of the B.C. Centre for Disease Control’s public health laboratory.
Herd immunity can slow or halt the spread of a disease when enough people are immune that the novel coronavirus can’t find anyone susceptible to infect.
So, knowing how many people have had the disease and are immune will be key to deciding when you can safely get your hair cut or play a pickup game of soccer.
The key to knowing will depend on finding a reliable serology test, one that can detect an immune response to the virus in people who have had COVID-19 and not known it.
When infected with a virus, the body produces proteins called antibodies specifically designed to bind to that virus, disabling it or marking it for destruction. Vaccines are made to stimulate production of those targeted antibodies in people who have never been infected.
The presence of antibodies is presumed to mean you are now immune to the virus and cannot get it again.
In some populations, such as those on cruise ships or communities in northern Italy, from 45 to 75 per cent of people who tested positive for COVID-19 had no symptoms at the time.
That means many thousands of us could have already had the virus and developed an effective immune response to it. We just don’t know who or how many.
“We are in the process of validating whether the existing serology tests are reliable,” said Krajden. “We hope to roll out testing for the purpose of supporting front-line health-care workers and then understanding the level of immunity in the population.”
Accurate serology testing will provide reassurance to front-line health-care workers, who must deal with the stress of daily contact
with patients who have active infections and people who may be infected, he said.
Provincial health officer Dr. Bonnie Henry is especially keen to let health-care workers know if they have the antibodies and that they are immune.
Knowing the level of immunity among all British Columbians will be key to deciding when and if to relax the physical distancing requirements needed to slow the spread of the virus, experts say.
“We don’t know how long the immunity lasts, but we expect it to be at least months,” said Henry.
Testing on primates suggests that once you clear the infection, you are immune to the virus, which is the case with closely related coronaviruses.
All the testing for COVID-19 to date has been focused on finding people who are actively infected with the novel coronavirus to determine who can transmit the virus to others.
Serology testing is more like election polling.
“You don’t have to test everybody, but you can get some estimate of who in the population has been infected and that will help us guide the relaxation of physical distance measures,” said Krajden.
American commentators have floated the idea of creating a COVID -19 certification system, or immunity passport, so that people who are confirmed to be immune can go back to their normal lives and their jobs in order to restart the economy as quickly as possible.
Krajden was cool to the idea, preferring to use such tests to keep the health-care system functioning smoothly and to inform policy makers.
The Public Health Agency of Canada’s National Microbiology Laboratory is working on developing a number of serologic tests and evaluating commercial serologic tests for COVID-19.
“This pan-canadian collaboration includes members of the Canadian Public Health Laboratory Network, clinical researchers from front-line health-care settings, and Canadian Blood Services, all of whom are working to establish the materials needed for both the evaluation and then implementation of serologic testing,” the Public Health Agency of Canada said.