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Are people getting immune to the Covid19 after they contract it and survive? For how long?
Question Date: 2020-10-26
Answer 1:

Alondra, you’re asking the important questions!

Because COVID-19 is so new, there’s still a lot that we don’t know about it. But we’re learning about it more quickly than any disease in history. The US Department of Homeland Security keeps a great list1 of key questions about COVID-19 (and SARS-CoV-2, the virus that causes it) and all the studies that have tried to answer them.

First, it’s important to understand that what we call “immunity” isn’t an on-or-off switch; it’s more like a sliding scale. Each person’s body is a little bit different, so the chance that they will have an immune response, and the strength of that response, varies a little bit from person to person.

With that said, the short answers to your questions are “yes” and “we don’t exactly know yet, but at least several months”.

The first question is relatively easy to answer. Scientists have checked the blood of thousands of COVID-19 survivors a few months after they recovered, looking for neutralizing antibodies, which are proteins that stick to SARS-CoV-2 and prevent it from infecting cells. They’ve consistently found that about 90% of survivors have those antibodies.

That doesn’t prove that those people are immune to reinfection, though—to test that, you’d have to expose those people to the virus and see if they get sick again. As much as we’d love to answer this question, it’s not worth putting people’s lives in danger! In cases like this, scientists perform experiments with other mammals, whose basic biology – including their immune systems — is similar to humans’.

Experiments using macaques, ferrets, and cats found that reinfection is possible, but not very likely. Only a few of the animals got sick a second time, and had only mild symptoms. This evidence should make us more confident that people with neutralizing antibodies probably are resistant to reinfection.

Your second question is more difficult to answer, mainly because COVID-19 has only been around for less than a year! (I know, it feels like it’s been much longer, doesn’t it?) Most COVID-19 survivors only recovered a few months ago, or less. Scientists who want to answer this question have to wait for time to pass, periodically testing COVID-19 survivors’ blood over time. So far, the biggest study to do this has found that the immune response lasts for at least four months.

If you’re impatient like me and don’t want to wait for years to find out when COVID-19 immunity will finally fade, you can look to SARS-CoV-2’s relatives for hints. You’ve probably heard SARS-CoV-2 referred to as “coronavirus”; in fact, “coronavirus” refers to a family of many different viruses that all have the same shape. Some of these viruses cause the common cold, and one of them caused the SARS-1 epidemic in 2003. Studies have found that immunity to common cold coronaviruses lasts about a year, and immunity to the SARS-1 virus lasted about two years2. It’s reasonable to expect that COVID-19 immunity will be somewhere in that range.

Now, you might be thinking, “Uh oh! Does that mean we’ll have a COVID-19 pandemic like this every couple of years?” No, probably not. There are a couple of possibilities. First, widespread vaccination may lead to the eradication of SARS-CoV-2. That’s what happened with smallpox, which was eliminated worldwide in 1980 and is still the only infectious disease ever to be fully eliminated3. You can see why vaccination is so important!

Alternatively, SARS-CoV-2 could become endemic, meaning that it could stick around and circulate in the population indefinitely, like the common cold or flu. In that case, COVID-19 would probably become less deadly over time. In fact, the other coronaviruses that cause the common cold probably started out this way, causing high mortality at first, then becoming milder as they coevolved with humans4.

A virus doesn’t “want” to kill its host; it just wants to make as many copies of itself as it can! Viruses that are too deadly can’t spread well, so they tend to evolve to become less deadly over time.

One last thing: you’ve probably heard news about people getting COVID-19 twice. There are only 24 confirmed cases of this happening so far5. If that seems like a lot, consider that over 43,000,000 people have had it once, and there are more than 7,800,000,000 people in the world. If getting COVID-19 twice in one year was very likely, there would probably be many more documented cases of it, so it’s probably not something worth worrying about too much. Instead, let’s focus on keeping ourselves and our loved ones from getting it the first time, which we can do by washing our hands, wearing a mask in public, keeping distance from others, and getting vaccinated when the time comes.

Thanks for your questions! Stay safe, and stay curious!

References by number:

1. United States Department of Homeland Security. “Master Question List for COVID-19 (caused by SARS-CoV-2).” October 20, 2020. link.

2. Wu, Li-Ping et al. “Duration of antibody responses after severe acute respiratory syndrome.” Emerging infectious diseases vol. 13,10 (2007): 1562-4. doi:10.3201/eid1310.070576

3. United States Centers for Disease Control and Prevention. “History of Smallpox.” August 30, 2016. link.

4. Bob Holmes. “How Viruses Evolve.” Smithsonian Magazine. July 17, 2020. link.

5. BNO News. “COVID-19 reinfection tracker.” October 27, 2020. link.

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