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What Do The Results From Antibody Testing Actually Tell Us About COVID-19?


Antibody testing could help determine whether someone has been infected with COVID-19 in the past. But there are still a lot of unknowns about what else we might learn from the tests.

Antonia Altomare is an epidemiologist and infectious disease physician at Dartmouth-Hitchcock Medical Center. NHPR's Morning Edition Host Rick Ganley spoke with her about what antibody testing does tell us about the spread of the virus.

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Rick Ganley: There are still many unknowns surrounding COVID-19 and immunity from the virus. Health officials, I know, have expressed uncertainty about whether having antibodies actually means immunity. How is having that information useful? What does it really tell us?

Antonia Altomare: Yeah, you're right. So what we don't know with confidence yet is does the presence of an antibody equal immunity? So does it mean that you cannot get reinfected with that same organism or that same virus?

So right now, all it really tells us is, yes, you have been infected, but we can't really know what to do with that yet as far as okay, if you have those antibodies, are you allowed to go out in public to work without using any particular precautions? So I think in the future, once we have more information about that, we'll be able to use it to understand what percentage of our population is now immune and able to safely kind of go back into the workforce. But right now, we don't have enough information to say that.

Rick Ganley: Is there any idea when we might have some of that information when some of that research will be done?

Antonia Altomare: So I think it's hard because right now, unfortunately, all the tests that are available, and there's many, many of them, they've got a 50/50 shot of being correct, which is not a great test at all. So someone who could have had the infection can get their antibodies tested, and it may not actually show that they had the infection 50 percent of the time. So until we have a better test, I think it's going to be really hard to know what to make of the results. And as far as the research behind immunity is concerned, that's ongoing and I think we're getting closer. I would say that probably in the next week to month, we'll have a better sense of what that antibody presence means.

Rick Ganley: But if you're saying that these tests are incredible, I mean, a 50/50 shot is basically leaving it up to chance. What does the test tell us at all?

Antonia Altomare: I think that's the big question. With any tests too, one of the big things that affects its predictive value, so when we're speaking in statistics terms, the lower the prevalence is of a disease in a population, the more likely you are to find a test that gives you a false positive. And I think in an area like New Hampshire and Vermont, where our percent positivity rate of all the people we're testing right now for COVID-19 is in the 3 to 4 percent range, that's pretty darn low. So any tests that you do in kind of this area are not going to be as accurate as one would hope.

Rick Ganley: Okay, so given all this, who would you recommend go out of their way to get an antibody test? Is it really worth doing it at this point?

Antonia Altomare: So the reason antibody tests are being done right now really are for kind of setting a prevalence rate. So it's for epidemiologic purposes to look at how much of our population has been infected. But again, keeping in mind that this may not be an accurate test to begin with. And so for me, I would say I probably have no reason to go out and get it. I think as society opens, and as we learn more and as we have better tests, I think it would be a way to get people safely back to work. Right now, certainly not in health care, are we saying even if you do get this testing, you are positive. And even if we know you've had COVID-19, we are still recommending all the appropriate precautions to protect them from getting reinfected because we just don't know whether having infection really make you immune.

Rick Ganley: So, you know, positive results or not you'd still recommend social distancing, mask wearing and so on?

Antonia Altomare: That's right.

Rick Ganley: Is there any benefit for the state to track the data resulting from antibody testing?

Antonia Altomare: You know, the state is the one that's really pushing a lot of the antibody testing right now. And I think from that level, it is helpful to kind of get some groundwork done with regards to what is our infection rate, if you will. And from the state level, the percent positive tests from the antibody tests are roughly matching up with the PCR testing, which is the test of active disease, the test that looks for actual virus. And so there's about a 3 to 4 percent positivity rate in both. So it's not widely different, but again, very small numbers. So I think with the more information we get, the more testing we do, we will be able to kind of validate those numbers better.

Visit NHPR's coronavirus news homepage for more stories

For many radio listeners throughout New Hampshire, Rick Ganley is the first voice they hear each weekday morning, bringing them up to speed on news developments overnight and starting their day off with the latest information.
Mary McIntyre is a senior producer at NHPR.
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