Antibody tests for COVID-19 are now available, but are they worth it?

Antibody tests are now available in Ontario but health experts and private labs are reminding patients that a positive test doesn't mean someone is immune — we still don't know if SARS-CoV-2 antibodies protect all people from getting COVID-19 again or from spreading it to others.

LifeLabs became the latest commercial lab in Ontario to start testing patients for antibodies on Nov. 23. Dynacare has been offering SARS-CoV-2 antibody testing in Ontario since Sept. 8, a spokesperson said Monday. Since August, the company has performed about 10,000 tests in Quebec and Ontario, half within the last month alone.

Both the serology tests offered by the companies do not detect an active COVID-19 infection but instead use blood samples to look for SARS-CoV-2 antibodies.

The tests promise to give some people an answer as to whether that persistent cough or scratchy throat a few months back was potentially COVID-19, but may not offer much insight beyond that. 

COVID-19 immunity remains murky

Marc-André Langlois, a University of Ottawa professor and Canada research chair in molecular virology and intrinsic immunity, said while a previous COVID-19 infection likely does provide some immunity, it's not clear how robust a protection that offers or how long it lasts.

"The scientific evidence is now showing that if you've been exposed and you've made antibodies, there's a good probability that you will be protected at least in the short term," he said.

"What no one knows, at this stage, is how long this protection from the antibodies will last."

The protection could span a few months or possibly up to a year, he said. What's more, it's not clear what protection actually looks like.

"We know reinfections can happen, they've been documented," said Langlois, adding that even if a patient had mild symptoms the first time around, they may not have the same outcome again. 

It's also possible the antibodies will not provide what's called sterilizing immunity, where recovered patients cannot pass on a virus to others, he said. In other words, someone with SARS-CoV-2 antibodies may still be able to spread COVID-19. 

'We're dealing with nuances' 

Ottawa Public Health recommends that anyone who tests positive for antibodies continue to exercise normal COVID-19 precautions, like physical distancing and mask wearing, and not to take a relaxed approach.

Public Health Ontario advises against the use of antibody testing for determining the immune status of patients.

Langlois doesn't envy public health officials who must both acknowledge that antibodies do seem to offer some degree of protection but not enough for people to let their guards down.

"We're dealing with nuances," he said. "That is the concern here, [an antibody test] provides people with a false sense of protection."

Costs of the tests

A SARS-CoV-2 antibody test at LifeLabs costs $75 while a test at Dynacare costs $70 and both are available in Ontario with a doctor's referral. The companies acknowledge on their websites that a positive antibody test does not mean a patient has immunity to COVID-19.

In some circumstances, Ontario Health Insurance Plan (OHIP) will pay for the antibody test, such as in children with multisystem inflammatory syndrome and patients with severe illness who have tested negative for COVID-19 repeatedly, and where an antibody test would be a "helpful adjunctive tool," Public Health Ontario says. 

For the most accurate results, LifeLabs recommends patients get tested between three and four weeks after symptoms or possible COVID-19 exposure but said antibodies have been found months after infection.

Dynacare says patients can get tested 14 days or more after an initial infection.