The era of civilian space travel has begun!

And if you’ve got a cool 55  million dollars lying around,   you too might be able to book a  multi-day trip into Earth’s orbit. Well, that’s what NASA pays per astronaut  heading to space via a SpaceX rocket, anyway.

If you’re famous enough, maybe  you could pay them in “exposure”. But before you drop any amount of cash, you  should know that space travel can make you sick. Because there’s a good chance that right now,   you have at least one virus that’s been  hiding inside of you for years, lying dormant.

And if you’re up in space long  enough, that virus will wake up. [♪ INTRO] Our immune systems, on the whole, are pretty good at clearing out viral infections. But some viruses have figured out a way  to evade our internal security system. One of the most infamous  is Varicella zoster virus,   which is the herpes virus that  causes both chicken pox and shingles.

You may have also heard of Epstein-Barr virus,  another kind of herpes virus, that causes mono. One of the reasons these viruses wind  up sticking around is that they often   infect parts of our body where the  immune system isn’t very active. Like our eyes, nerves, and brain.

Or, they infect our immune system itself,  preventing it from functioning normally. Another reason is that these viruses  typically don’t kill the cells they infect. In some viruses, killing a cell is part  of the virus’s normal “life” cycle.

If you consider viruses to be alive, which is  a debate that we don’t have time for today. It’s a part of how they replicate  and spread is all I’m trying to say. But in most viruses, infected  cells are going to die either way.

Because when a virus infects a cell,  enzymes inside that cell will chop off   little bits of the virus and discretely  move them to the outside of the cell,   where they can sound the alarm: “I’m infected!” Then, our immune system swoops  in to tell that infected cell   to sacrifice itself through  a process called apoptosis. But some viruses, like varicella and Epstein-Barr,  have found ways to prevent infected cells from   letting the body know they’re infected, protecting  themselves from being cleared out of the body. These viruses then hide their  genome, or genetic code,   inside the cell’s nucleus…which you might  remember is where we store our genetic code.

That’s where my code is, don’t put it in there! Our cells do fight back, though. They immediately silence the virus’s genome  by winding it tightly around proteins,   preventing it from being read.

The virus enters Sleep Mode, or if  you’re a scientist, a latent phase. But the virus is still there,  meaning we are still infected. Basically for life.

And it can reactivate periodically, producing  new viruses and causing all kinds of symptoms,   from mild rashes to life-threatening disease. We don’t fully understand what causes  these sleeping viruses to reawaken and   make people sick again, partly because  it’s a little different for each virus. But evidence is mounting that it has to do  with our immune systems and cellular stress.

When cells are stressed, say,  by getting a little too hot,   or getting exposed to the  wrong kind of solar radiation,   these proteins that normally clamp down on a  virus’s genetic code can loosen their grip. And this opens the door for some viruses  to use their code to make new viruses. Still, if they reactivate,   our immune system can swoop in and  clean up any sneaky virus production.

But what if our immune system  isn’t working properly, either? Well that brings us to space herpes. Scientists first noticed this “space travel  reawakens sleeping viruses” phenomenon back in   the late 1990s, when virus particles  showed up in astronaut saliva.

At first, the increase in virus  particles was only observed in   samples collected before they headed  up to the International Space Station. So researchers figured it might be due  to stress leading up to the mission. The typical kind of stress you think about.

Not cellular stress. But just  getting-ready-for-your-space-mission stress. Because stress can affect your immune system.

But in follow-up studies, virus particles  started appearing in samples collected   during the flight that hadn’t  been present before takeoff. Researchers hypothesized that this was  part of acclimating to space and that   virus levels would taper off eventually, as  the astronauts got used to their environment. But the opposite happened.

The longer astronauts were in  space, the more virus they shed. That’s not great for missions to, say, Mars,   which would require as many as nine  months of space travel each way. But until someone invents some kind  of interplanetary teleportation tech,   we can’t remove space from the  “Let’s go to Mars” mission plan.

So we have to understand what it is about  space travel that reawakens those viruses. And that is where things get tricky. Space is a mess of overlapping  independent variables.

Throughout a mission, astronauts  deal with isolation, microgravity,   psychological stress, disrupted sleep  schedules, cosmic radiation, and more. And they often endure several of these at the  same time, making it difficult to tell whether   it’s the microgravity, the lack of sleep,  or something else causing the problems. But scientists have researched  these as independently as they can.

For example, stress hormones and  microgravity have both been shown   to make cells stressed and  suppress the immune system. Meanwhile, loneliness, inadequate sleep,   and cosmic radiation all seem  to make some viruses reactivate. So it looks like maybe the  answer is “all of the above”.

So the question becomes: What are the  risks of these viruses reactivating,   no matter how they manage to do so? But before we can answer that  question, we have to show you an ad. Thanks to Brilliant for  supporting this SciShow video!

Brilliant is an online learning platform where you  can build knowledge through interactive lessons. It’s the kind of learning where you can  expand your horizons at your own pace. You’re not limited to a  traditional classroom schedule.

And if you only have a moment,  Brilliant fits into your life. With Brilliant and a smart phone,  you can learn any time, anywhere. In a waiting room, on a train platform, on a date… Well, maybe not on a date.

But if they’re still getting ready,   you could learn algebra and Python  before they find the right shoes. To try Brilliant for free,  visit brilliant.org/scishow,   scan the QR code onscreen, or click  on the link in the video description. You’ll also get 20% off an  annual premium subscription.

According to a study published in  2017, eight of the 23 astronauts   in their sample were shedding some or all  of the viruses the researchers looked for. But only one of those astronauts had  any documented symptoms, including an   annoying but mild rash that managed to  appear on two separate trips to space. I know that 23 is not a particularly large  sample size, but that’s one of the problems   with researching the effects of space on the  human body: not many people have gone to space.

Even if it is true that about a  third of astronauts will have a   virus reactivate while they’re in space,   it’s likely that a much larger percentage of  them have these viruses hiding inside them. For example, a 2013 study found that 54% of  14-to-49 year olds in the US have oral herpes. Meanwhile, a 2021 paper reported that  a whopping 97% of men between 18 and   70 across the US, Brazil, and  Mexico, had Epstein-Barr virus.

And that’s basically as common  as chickenpox-causing varicella,   although that statistic is probably  lumping in everyone who got the vaccine,   too, which relies on a live but weakened form  of the virus that will also stay inside you. Which, not so fun fact, can also  reactivate and cause shingles,   but has a much lower chance of doing  so compared with the regular version. Since longer space missions mean more exposure  to all of these space-related stressors,   it could mean that way more than a third  of astronauts will have a virus reactivate.

And healthy astronauts don't seem  to wrestle these infections back   into sleep mode as easily as  healthy people on Earth do. And that brings its own risk. Even ignoring research that shows  an association between repeated virus   reactivation and diseases like  Alzheimer’s, it increases the   odds of someone on your crew having a very  rare, but very dangerous health emergency.

For example, if herpes takes a wrong turn and  goes up to your brain instead of down to your   skin, it can cause a life-threatening  brain infection called encephalitis. And our spaceships don’t come  with fully stocked sick bays,   led by grouchy but passionate  Georgian chief medical officers. So right now, our best bet is  to make sure space travelers   are not in that situation in the first place.

Space health researchers have a bunch  of strategies that work together,   kind of like a stack of swiss cheese. Each layer of cheese stops some of  the causes of virus reactivation. The first layer stops the problem  before it starts: candidate screening.

Because certain people are more likely to develop  severe infections based on their genetics. And scientists are actively researching  how to predict who those people are. Screening for those people at risk  can keep them out of harm’s way.

And for the astronauts that do get selected,   scientists hope to run them  through a sort of stress test. For example, a months-long mission  to Antarctica during winter’s   eternal night to test their immune systems. While not perfect, these pre-flight  missions simulate similar levels of stress,   danger, and resource scarcity as an  astronaut would experience in space.

And researchers have already observed  changes to the subjects’ immune systems,   and an uptick in the amount of virus  they were shedding during these missions. Some even had mild symptomatic infections. The second layer of cheese is personal prevention.

For example, whenever possible, future space   travelers should get vaccinated  to prevent severe infections. They should make sure they’re  getting enough of the right   nutrients to prevent things like vitamin  deficiencies, and getting enough cardio,   because astronauts with better cardio  fitness shed less virus in space. Another layer of cheese is pre-flight quarantine,   to minimize the number of viruses  astronauts bring up with them.

And finally, there are modifications to  the spaces astronauts will be living in. By installing better filters to eliminate  airborne microbes, or shields that block   more radiation, engineers can help reduce the  stressors that trigger virus reactivation. Collectively, all of these   layers of cheese should go a long way  toward protecting astronauts’ health.

But let’s be real. Based on current research,  reactivation seems pretty inevitable. Eventually, someone is going to get  sick on a long-term space mission.

So one of the best things  we can do is be proactive. Regularly measure every astronaut’s blood  and saliva so we know as soon as possible   when their immune systems are out of wack. NASA is already doing that  at least to a certain extent.

If viral particles start  popping up in their saliva,   or if we detect it in the air, the crew  could start an antiviral therapy asap. Antivirals are like antibiotics, but for viruses. One topical example is Paxlovid, which makes  people less likely to be hospitalized from COVID.

Will all these measures be enough  to protect people in space? Who knows. And there may be problems we haven’t seen yet.

The laws of evolution don’t stop  at the edge of Earth’s atmosphere. Viruses could evolve new ways to harm  us in space, like some bacteria have. But this framework gives us a starting point.

Still, I’m not particularly jazzed  about the idea of my dormant chickenpox. So I might have to hold off on space travel  until scientists have learned a little more. Although, I’m turning 50 in five years  and then I get my shingles vaccine.

That’s right. And you should too. So that’s why, for now, I’m not going to space   and it’s totally not because I  don’t have 55 million dollars. [♪ OUTRO]