A small study from China that followed 37 positive but asymptomatic people just produced some disappointing results.

Antibody levels against COVID-19 were far lower and even nonexistent in asymptomatic individuals compared to those who had obvious symptoms of the virus. As well, antibody levels fell more quickly in those who never showed symptoms.

A University of Toronto professor told CBC that it would appear from this small study published in Nature that a past COVID infection may not confer lasting immunity. That means that herd immunity isn’t something we can count on to protect the majority of populations that haven’t been infected. It also means those who’ve already had COVID could theoretically get sick again if their immune system lacks a memory.

Studies like this one mean that serological blood testing – also known as antibody testing, may have limited clinical value. Alberta has become the first province to announce a program for antibody testing. In B.C., the main point person on antibody research and testing is Dr. Mel Krajden, medical director of the BCCDC Public Health Laboratory. I spoke with him at length; here’s a condensed, edited version of our conversation.

Where are we, at this point in time, with antibody testing? Everyone is anxious to know if it will be useful for determining the prevalence of COVID-19 in our communities.

We’re part of the national team working on this. We’ve been trying, in a nutshell, to test and validate a bunch of commercial assays. Many are performing reasonably well, with high specificity and sensitivity. Some people don’t make antibodies at all, or less if they have had mild infections.

There’s a lot of emotion when it comes to immunity since people want to think they have protection (against reinfection) once they’ve had COVID but no one yet knows the durability of protection. (Medical experts) are fearful about this notion of immunity passports because what we don’t want is people no longer physically distancing or having a false sense of security. This is a challenge from a public health perspective. You don’t want to mislead the public about the potential for antibody testing.

Serology tests should be seen as just like a little blanket you go to bed with; it’s not that protective.

So what is the main goal for antibody testing?

Serology is important to determine seroprevalence in communities. Quebec and Ontario will have a higher prevalence in dense cities like Montreal and Toronto. It’s useful to know if someone who is seropositive actually has some degree of protection. With other coronaviruses, antibodies hang around for some time but no one knows for sure with COVID.

So really, it has limited value. It can tell you the proportion of the population that got infected, that’s the value. It can also identify people who are sero-protected and then we can study them longitudinally. I would caution people using it for emotional use. Some people don’t make antibodies but for those with them, it shouldn’t be seen as an opportunity to say ‘I’m home free. I’m protected and I don’t have to worry about getting it.’

I’ve heard of some Canadians who’ve been paying for antibody testing (blood samples are sent to private labs in California and elsewhere.) I imagine companies like LifeLabs may want to offer it to private companies. What are the harms?

I would say no one should think they are home free. The messaging that goes with the lab results should be honest about the limitations. It should come with caveats.

Is it a wise investment for companies or the general public?

I don’t think it’s crucial. But for governments, it’s worthwhile to know what proportion of the public has been infected. We are looking at this now among health care workers. (Previously, Krajden said that such information about immunity and antibody levels could be reassuring to health care workers).


Have you chosen the test or tests you will use in B.C?

We’re still figuring out what test is best so we can land on the most responsible solution. We’re evaluating about a handful, including ones from Siemans, Roche, Abbott and Ortho.

We’ve done some testing on health care workers and some other groups who volunteered for this kind of research months ago and now we want to make sure we trust it.

We worked with public health, sought volunteers like health care workers in long term care facilities. We know the time frame they were diagnosed and now we are able to see the behavior of the test over time.

I wrote an article about how 25% of health care workers had been infected with COVID up to June 8 which seems really high and I guess it’s even higher now. There were 662 when I wrote the story.

Well the challenge with health care workers is that they are all more likely to be tested because we need to know if they should not go to work and the value of personal protective equipment, etc. Numerically, the number you cite is correct but the true proportion who got infected at work, or traveling on transit or in their homes and community settings, we don’t know.

We oversampled health care workers. I guess my feeling is that PPE works so as long as it’s used and used responsibly. I don’t think the risk to average health care workers is incredibly great. I don’t think they are tremendously or disproportionately at risk.

So how and when will antibody testing be rolled out?

At first, it will be directed to seroprevalence, then we may use it for some diagnostic dilemmas. We have to try to get Canadian consensus on the best uses of it. I would bet we’ll be rolling out a program within a month but it will involve very specific populations since, at this point, serology is not for prime time use.

We know safe and effective vaccines are our best hope. Dr. Anthony Fauci has said that he thinks vaccines may only provide protection for months which means we might have to get vaccinated a few times a year.

Yeah, I mean nobody knows that at this point. I think he’s thinking out loud. I like Fauci, he does a great job, but no one has a crystal ball.

Twitter: @MedicineMatters