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Weekly Update On The Science Of COVID-19: Antibody Testing


Antibodies are an immune response that linger in the blood of people who’ve recovered from a disease. That’s also how vaccines work—they teach the body how to produce those antibodies so it’s ready the next time the disease comes around. There’s no vaccine for COVID-19 yet, but scientists have developed blood tests that can identify antibodies against coronavirus. In KNAU’s weekly update on the science of COIVD-19, Melissa Sevigny spoke with infectious disease expert Dr. Paul Keim about why these antibody tests matter for public health, and what it means when the results say someone is “sero-positive.” 

What is antibody testing and how does it work?

It’s a blood test, and it goes in and looks for these proteins that your body produces to protect itself from the virus. Antibodies are part of our immune system, and they get stimulated after your exposed to the pathogen, or when you get vaccinated…. These antibodies come in many different types but the earliest we see them is really about 2 weeks after you’ve been exposed to the virus.

So how long do the antibodies last in your system?

We don’t know yet. This is a brand new disease. We don’t really know how long the coronavirus antibodies are going to last in our system…. But in some cases antibody responses can last decades. There are certain vaccines, for example, that you only need a booster every 10 or 20 years. But in other cases we need a booster, a new vaccine, every year.

So what can this kind of testing tell us about the pandemic?

From a public health standpoint in how we manage this pandemic, the sero-positivity rates are really important. When I use the word “sero-positivity,” I mean you have antibodies in your blood against that virus…. We know for example the antibody testing that’s been going on in New York City that 20 percent of the people in New York City are now carrying antibodies to the coronavirus…. In Arizona right now numbers are much lower. The Arizona State Department of Health dashboard, for example, is reporting 3.1% positive rates… Now the other thing that these numbers tell us is that we’re not detecting all of the cases. For example, the Arizona state dashboard was reporting 37,000 cases reported in Arizona. But if you use that 3.1% sero-positivity, you’d actually come up with a number that’s more like 200,000… The great discrepancy between the reported cases and the estimates from antibody tests really do indicate there are a lot of asymptotic or at least low-symptom type cases going on that are not making their way into the official reporting system.

So that might mean that the disease—a lot of people have mild disease, they’re not really noticing the symptoms, and therefore might be out and about and spreading it, is that right?

That’s absolutely true. We know that people who are asymptotic can be shedding a lot of virus and can be spreading the disease… The other thing we’re beginning to understand that the mortality rate of the disease can be overestimated, if we don’t actually know what the asymptotic rates are.

What does this testing mean for individuals—if I went out and got this test and it was a positive result, what would that mean for me?

If you test positive, most likely you had COVID-19…. There’s a little bit of just personal knowledge there, everybody likes to understand what’s going on with them…. Now of course if you test positive everybody’s wondering: does that mean I’m protected and I can’t get the disease again? And the answer is, we don’t know yet. We hope that’s the case. It’s the premise for all the vaccination programs that are going on in the world… but we don’t know for sure. We’re so early in this pandemic that the data are just now coming in. I will say there are studies from animals where animals have been infected with the virus or vaccinated with viral parts, and those animals are resistant to further infection. So I’m absolutely hopeful that sero-positivity will be correlated with some level of protection. How protected and how long are still unanswered questions.

Paul Keim, thanks so much for speaking with me.

You’re welcome, Melissa.

The University of Arizona is unrolling a statewide antibody testing program, which is currently limited to healthcare workers and first responders. Tests are also available through Sonora Quest Laboratories and health care providers. 

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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