This episode was shot on September 15th, 2020.

If we have any updates to share, we'll include them in a pinned comment. And, as always, you can find the most recent COVID-19-related episodes in our playlist linked in the description. [ intro ].

One of the big questions in this pandemic has been whether or not getting COVID-19 protects a person from getting it again in the future. For some viruses—like measles— infections are essentially one and done. Once you have the disease, you never get it again.

But for others, like hepatitis C, reinfections are common. The body just doesn't seem to develop a good enough memory of the virus to stop it when it shows up again. And everyone has been wondering where on this spectrum the virus behind COVID-19 falls.

Well, new reports say yes, you can get reinfected with this new coronavirus. But initial infections may still be protecting people from the disease, because not all reinfections are bad. One of the things muddying the waters here is that people use the term “reinfection” pretty loosely.

It refers to any time a person gets the same virus twice. It doesn't tell you whether a person got the disease twice. And that does not sound like an important distinction, but it is, because technically, reinfections are a normal part of immunity— even with “one and done” viruses like measles.

That's because, as good as your immune system is at spotting and destroying pathogens it knows, it's not instantaneous. The odds that you'll grab and stop every single infectious virus that enters your body before it can start replicating are slim to none. What your body can do, though, is target and destroy pathogens and infected cells more quickly on subsequent exposures.

So even though you get briefly reinfected, you don't show any symptoms— and ideally, you're not contagious. That's what everyone is hoping for with SARS-CoV-2, the virus that causes COVID-19. Early on, some experts were worried that reinfections were common because people kept testing positive, then negative, and then positive again.

But that could come down to issues with testing. Or it could be a phenomenon called reactivation, where viruses just kind of hide out for a bit and then emerge and replicate again. To really know that a reinfection has happened, you have to show that the second infection differs slightly from the first, so you're sure it's not the same infection being re-detected for some reason.

And that's what researchers in Hong Kong found. Authorities were carefully testing travelers as they came and went. And a 33 year old man—who'd previously had COVID-19 and recovered— happened to test positive again.

The two infections were about four months apart, and the genome sequencing revealed that the new infection was a slightly different strain of the virus. So he really did get SARS-CoV-2 twice. But the good news here is he showed no symptoms the second time around.

As far as researchers could tell, his immune system was doing exactly what you would want: it launched a swift counterassault when it saw the virus again, and presumably, kept it from harming him. Now, it isn't clear if he was contagious at any point during the second infection. If he was, then silent reinfections could contribute to the spread of the disease.

But this case does suggest a first infection can confer some level of protection against later ones. Unfortunately, a separate case from Nevada was the exact opposite. A twenty-five-year-old man had a mild case of COVID-19, recovered, and then contracted a slightly different version of the virus less than two months later.

And that second infection landed him in the hospital. The write up of this case still needs to undergo peer review, but if the findings hold up against scrutiny, they'd suggest that prior infections don't always confer protection. It's even possible people are more likely to have a severe case the second time around.

That's something that happens with dengue viruses, for instance, and one feline coronavirus that we know of. So people are concerned it could happen with this coronavirus, too. Unfortunately, right now, and I'm sorry that we say this so much, we do not have enough information on reinfections to determine how common they are — or, when they do happen, whether the second infection is more likely to be mild or severe.

Although we can say for sure, and this is new information. Is that they can happen. So, until the experts figure all this out, people who've had COVID-19 should continue to protect themselves.

And other people around them with measures like washing hands, wearing face coverings, and physical distancing. Thanks for watching this episode of SciShow, which was brought to you by this month's President of Space, Harrison Mills. Your support is helping us keep people informed and up to date — so thank you.

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