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Just about a year ago now, we first heard of a new, potentially dangerous coronavirus. And now, in some ways, it feels like we know it all too well.

And we do know a lot more than you’d expect only a year in. But there are also some big, enduring mysteries — including these three. First up: why some people get way sicker.

Like with most respiratory viruses, we know certain people are at a much higher risk of having a severe infection of COVID-19— those over the age of 70, for instance, or who belong to vulnerable racial and socioeconomic groups. But even within normally low-risk groups, cases run the gamut from no symptoms at all to rapid lethality, and no one is sure why. There’s been a long-standing hypothesis that part of this variation comes from the amount of virus the infection starts with— that people who breathe in more are more likely to get really sick.

This has proven difficult to study in the past, but thanks to modern medical science, we might finally be able to figure out if it’s true—for COVID-19 and other diseases. So, that’s one thing researchers are planning to look into more this year. But another is genetics.

Immunologists have long suspected that people can be born with a tendency to have particularly mild or severe symptoms to a given infectious disease. And they've already linked some genetic variants to differences in immune function that may explain why some people end up in the ICU with COVID-19. Like, in an October 2020 study in Science, researchers found that people who got the sickest were more likely to have mutations in genes that affect type 1 interferons.

These are a group of immune proteins that are crucial for fighting viral infections. But we still have a lot more to learn about how genetic differences affect COVID — intel that could help predict how sick a person is likely to get and figure out the best drugs for them. There’s also mounting evidence that problematic antibodies play a role in all this.

Antibodies are normally helpful immune proteins that latch onto pathogens and, ideally, neutralize them. But sometimes, they misbehave and attack the person’s healthy tissues instead. And in some people, the virus that causes COVID-19 seems to trigger the formation of these self-attacking antibodies.

Like, ones that attack serum proteins, leading to sticky blood that clots too easily. Or, ones that attack those important type 1 interferons — which causes basically the same problem as mutations in those genes! And there’s also something weird going on with neutralizing antibodies.

Those are the kind we usually want, as they, well, neutralize pathogens and help a person fend them off. But a November 2020 study in the journal Nature Immunology found that adults with severe COVID-19 have more neutralizing antibodies than kids with milder infections. One explanation for this could be that kids’ immune systems are primed to fight off pathogens they’ve never encountered.

That may put them at an advantage against new pathogens in general, allowing their bodies to spot this virus and kick it out fast — before really ramping up antibody production. And confirming this could point towards ways of helping us grownups. But it could also be that neutralizing antibodies just aren’t as helpful as we’d think, for reasons that are currently unknown.

Next, antibodies also play a key role in our second big question that scientists will continue to investigate this year: how long immunity to COVID-19 lasts. With some viruses, surviving an infection confers life-long immunity. The body essentially learns to spot it and eliminate it fast if it ever shows up again.

But with other, related cold-causing coronaviruses, you can get reinfected in a matter of months. Where COVID-19 falls on this spectrum isn’t clear. One way scientists can get a hint at how long immunity lasts is by looking at how long neutralizing antibodies stick around, as these often play a pivotal role in clearing an infection.

One study of over 30,000 mild-to-moderate COVID cases found that, for the most part, neutralizing antibodies stuck around for about five months after the people got better. But this wasn’t true of everyone, and for those who did have these antibodies, it wasn’t clear how much longer they’d last. Plus, as we just talked about, these antibodies may not help us as much as we’d expect.

And also: antibodies aren’t the whole story when it comes to immunity. People who don’t seem to make antibodies at all may still be protected from COVID thanks to white blood cells called T cells, which also help fight infections. But those are even more of a black box.

Understanding immunity to COVID-19 is important because it can help us develop better treatments, and it might even give us clues as to how effective or enduring vaccinations may be. And lastly, researchers are hoping 2021 will shed some light on the long-term effects of COVID-19. Already, we’ve seen the emergence of “long-haulers” — people whose fatigue, pain, and heart and lung issues continue for months after they’ve gotten over their initial infections.

Other people who have recovered report experiencing brain fog, continued loss of taste and smell, dizziness, and confusion. But it just hasn’t been long enough for scientists to observe what happens to most people more than a few months post-infection. So until we get more data, we won’t know how common any of this will be, or when or if these lasting symptoms will go away.

And on top of lingering symptoms, COVID infections may have knock-on effects, like triggering or exacerbating chronic health conditions. For instance, some experts are worried that inflammation and other impacts on organs could contribute to brain deterioration and speed the development of conditions like Alzheimer’s disease in some people. Now, this all might sound bleak, but the good news is, 2021 will only bring a deeper understanding of this brand-new virus and what it does to our bodies.

That knowledge will help us best prioritize resources, weigh mitigation strategies, and ensure doctors can provide the best care possible to people with active infections and survivors. Thank you for watching this episode of SciShow News! We’ll be here every Friday this year to keep you up to date on the newest scientific discoveries, coronavirus related or not.

Every other day of the week we’ll tell you something new about the way this amazing world we live in works. And you can keep up with all of our episodes by clicking that subscribe button and ringing the notification bell. From all of us here at SciShow, we hope you have a healthy and happy new year. [♪ OUTRO].