IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, we’ll talk about the microbes that make your smelly cheese, and we’ll chew over the future of meat. But first, if you’ve recovered from COVID-19 or tested positive for antibodies, you might be wondering, can I get infected again? You might have seen reports in the news saying antibodies wane within a few months. You might have also heard about cases of reinfection and then skepticism about those claims.

So what’s the deal? Can you get COVID-19 twice? And if immunity does wane over time, how long would a vaccine protect us? Here to tell us more, Science Friday Producer Elah Feder. Elah, welcome back.

ELAH FEDER: Thanks for having me.

IRA FLATOW: So you started working on this story after your friend got COVID-19?

ELAH FEDER: Yeah, so back in May, my good friend got tested for SARS-CoV-2 antibodies. If you remember, New York had just started offering these antibody tests for free, and so a lot of people were getting them. I tested negative, but my good friend, whose name I’m omitting for privacy, she tested positive.

WOMAN 1: Which was surprising, because I hadn’t had any symptoms that I knew of. Like, I was thankfully very healthy.

ELAH FEDER: She’d actually been training for a half-marathon all throughout that spring, just in great health, so she wasn’t expecting this result. And just to be sure, she actually got a second test at another facility. And again, she was positive for antibodies. At the same time, she tested negative for the virus, and then negative again for the virus a few months later. So by all accounts, she’d had an asymptomatic COVID infection and cleared it.

And I was really excited by this. I thought, my friend is probably immune to COVID. She can walk around freely in a way that most of us cannot. I think I even joked that she was immortal.

That was incorrect. In October, I get a text from her that says she has COVID again. Thankfully, it was a mild case.

WOMAN 1: No fever at all, just a little bit of stuffiness and congestion. I think after about a week of having just a cold, I started to get, like, tightness in the chest. It kind of came and went.

ELAH FEDER: And that just lasted for a few days, and then you were completely fine?

WOMAN 1: Yeah.

IRA FLATOW: And so she’s all better now?

WOMAN 1: Yeah, she’s feeling great now. But for a few months, I was operating under the assumption that my friend was probably immune to COVID-19. I was in closer contact with her than I would have been otherwise. And clearly, I was wrong.

So I wanted to know, first, what do antibody tests really tell us? And what do we know about reinfection cases at this point? Are they really happening? I talked to a few experts, and the answer to that last question is yes.

AKIKO IWASAKI: There are confirmed cases of re-infections.

ELAH FEDER: Akiko Iwasaki is a professor of immunobiology at Yale, and she recently reviewed four confirmed cases of reinfection in The Lancet.

AKIKO IWASAKI: The first case was from Hong Kong, a man who was detected for the re-infection because of airport screening. But this was actually a good result, because this man had a mild infection the first case, and the second infection also resulted in asymptomatic infection. But then, there are other cases where the second infection actually resulted in worse disease than the first infection.

ELAH FEDER: One case was a 25-year-old man in Nevada who had mild symptoms in April. Six weeks later, he got infected again, and that second time, he was actually hospitalized. So a second infection can be very serious.

IRA FLATOW: So how do we know those patients are really getting infected twice? Could something else be happening?

ELAH FEDER: Right, so the question is, were these people maybe infected the whole time and just had a second flare-up of symptoms? Or was there possibly some mistake with the testing? And in these four cases, the main line of evidence that this is really, truly reinfection is that researchers actually sequenced the viruses, and they found that the virus from the first infection and the virus from the second infection were slightly different.

Now, even though there are only a handful of confirmed reinfection cases in the whole world, it actually shouldn’t totally surprise us that this can happen.

ALESSANDRO SETTE: In reality, that is very similar or reminiscent of what happens with common cold coronavirus

ELAH FEDER: That’s Alessandro Sette, a professor at the La Jolla Institute for Immunology. And you heard he mentioned common cold coronas. You might know that there are actually seven types of coronaviruses that infect humans.

There’s the virus that we’ve been talking about, SARS-CoV-2. There is the other, older SARS virus. There’s MERS, Middle Eastern Respiratory Syndrome. Those are all very serious. And then there are the four viruses that basically give you a regular cold. And we know that with those common cold coronaviruses, immunity is relatively short-lived.

ALESSANDRO SETTE: Because there are studies where people have actually experimentally infected people in the ’90s.

IRA FLATOW: Age 90?

ELAH FEDER: No, the 1990s, in the UK.

IRA FLATOW: Aha, I get.

ELAH FEDER: I didn’t know that this was allowed– experimentally infecting people with viruses. But I guess if they’re mild enough, you can get approval. But in any case, in this one study, researchers infected a few people with this common cold coronavirus, and then they exposed them again to the virus one year later, and six out of nine subjects did get infected again.

ALESSANDRO SETTE: But nobody got sick. So yes, we could have just enough virus to be detected, but nobody reported common cold symptoms.

ELAH FEDER: So that’s, obviously, a good thing. But reunification did happen.

IRA FLATOW: So what I’m wondering is, how do our immune systems respond to this coronavirus? We heard him talk about the other cold viruses. What about this coronavirus? Do our bodies remember it a few months later?

ELAH FEDER: Right, so a few months back, we saw some reports that suggested COVID-19 antibodies were declining pretty quickly, which sounded worrying to a lot of us. But there have been conflicting reports, and I asked Alessandro’s colleague, Shane Crotty, who is also an immunologist, about this.

SHANE CROTTY: So I’d say the area is controversial still. My take on the literature is that most of the studies are showing antibody is maintained pretty well, actually, and maintained pretty normally compared to other infections. Normally, there’s some drop after the end of the infection, but not a dramatic one.

ELAH FEDER: And this is important. Even if antibodies do decline, that doesn’t necessarily mean you’ve lost immunity.

SHANE CROTTY: One way that I’ve explained this is, actually, the hepatitis B vaccine, where it’s known that if you have antibodies after the hepatitis B vaccine, you’re protected from hepatitis B. And that’s great. But those antibodies fade after 5 to 10 years. And actually, the epidemiology has been those people are still protected, even though the antibodies are gone.

ELAH FEDER: Because when it comes to fighting and remembering infections, there are other parts of your immune system that are important.

ALESSANDRO SETTE: Antibodies are a component from it, but the immune system works in a way that you get infected, you have your immune cells that expand and reproduce, and then they contract. And they remain, to a certain level. And so, if you were to encounter that virus again, even though, maybe, antibodies have waned, those memory B cells are still there and then can start to make antibodies again on a moment’s notice.

IRA FLATOW: So if I understand what he’s saying, he’s saying the current presence or absence of antibodies is not a perfect measure of immunity at any given time.

ELAH FEDER: Right, exactly. So reinfection is, obviously, something we’re concerned about, but something that especially worried a lot of people when we heard about these cases is, what does it mean for a vaccine? If your body just cannot remember this virus for very long, you know, will your body mount an immune response to that vaccine and then forget a couple of months later?

AKIKO IWASAKI: Right, so the type of immune response generated during natural infection with SARS-CoV-2 may be different from those that develop during a vaccine response. And the reason for this is that the coronavirus, as with any viruses, they employ a lot of evasion mechanisms.

ELAH FEDER: So an actual virus is trying very hard to hide from your immune system, to avoid triggering antibodies, or B cells, or T cells.

WOMAN 1: Whereas vaccines don’t succumb to the same sort of evasion mechanism at all. It’s designed to promote the most robust antibody responses by stimulating both innate and adaptive immune responses and longer-lasting, hopefully, immune responses. So I don’t think any of these reinfection cases should equate to worries for vaccine-mediated immunity.

IRA FLATOW: Let’s hope not. OK, COVID reinfection is happening. Now, how common is it?

ELAH FEDER: OK, so it’s hard to know exactly. Some cases that look like reinfection might not actually be, like we mentioned. On the flip side, with cases of real reinfection, a lot of them might be getting missed.

Akiko mentioned earlier that case in Hong Kong. The patient got infected a second time, but he didn’t know it because he had no symptoms. The only reason that this got caught was because he happened to get tested at an airport. So without a proper epidemiological study, we don’t really know how common reinfection is. But Akiko is hopeful.

WOMAN 1: Well, I would think it’s fairly rare, even though, like I said, there is a caveat that reinfections may be occurring a lot more frequently, but because we don’t have the viral sequences from the two infections, it’s difficult to prove it. But I have heard of a lot of anecdotes, as your friend’s case, where a person recovers from an infection and then, months later, tests positive. So it’s probably occurring, but not very frequently.

IRA FLATOW: Great, let’s hope so.

ELAH FEDER: But, Ira, before we start giving out those antibody passports, remember that there can still be false positives. You know, you think you have antibodies, but you do not.

ALESSANDRO SETTE: And so you could have a significant fraction of the people that think they have a positive test, and thereby we think that they are protected, taking very significant chances. And so that’s kind of like driving a car with an airbag that you think it works, but there is no airbag. So that’s a little scary.

ELAH FEDER: So I read, do not make the mistake that I did. Do not assume, because your good friend has antibodies, that they are definitely immune. They could be harboring lingering virus. They might have gotten a false positive. They might get reinfected. So my final message is to stay vigilant.

IRA FLATOW: Good words of advice, Elah.

ELAH FEDER: I think so. Thanks, Ira. And I want to thank our guests. Akiko Iwasaki is a professor of biology at the Yale University School of Medicine. Alessandro Sette and Shane Crotty are professors of Immunology at the La Jolla Institute for Immunology. And I also want to Thank Neal denHollander, a retired immunologist in Mississauga, Ontario, for helping me with my research.

IRA FLATOW: And thank you, Elah. Elah Feder, development producer at Science Friday. Great report.

Copyright © 2020 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/