Hi, I'm John Green and this is a slightly different episode of Crash Course.

We’ve   heard from so many teachers and students who are  using Crash Course videos to help with learning   amid all this uncertainty, and we are really grateful. We’ve also heard from many of   you just how difficult it is to learn and teach  right now.

This has made everything difficult.   These days, “it” and “this” are often pronouns  that require no antecedent, but I’ll define   them anyway: Covid-19, a disease caused by the  SARS-CoV-2 virus, has spread across the entire   human community. In the first seven months of  this pandemic, more than a million people died of   Covid. Many people are out of work, and millions  are learning from home or learning in school   environments that may feel--and may be--unsafe.

And because the virus spreads through humans doing   things that used to be considered  normal--sharing a snack, sitting in   enclosed spaces with other people, talking  with friends--the way we interact with each   other has shifted dramatically and suddenly . When I think about disease and its treatment,   I usually first think about, like, medicines  and vaccines. If I think a little harder,   I might consider medical devices--ventilators,  dialysis systems, and so on.

But disease is not   only treated by those interventions. Similarly,  I tend to think of infectious disease as being   inevitable, which in some ways  it is--but only in some ways.   Like, take cholera, for example. It is accurate to say  that cholera is a disease caused by the bacterium   Vibrio cholerae, which infects humans who drink  contaminated water or eat contaminated food.   And it is accurate to say that the disease  is preventable via vaccine and treatable   with rehydration solutions and antibiotics.

But it is also accurate to say that cholera   is caused by humans--we spread the disease  to each other, and it spreads because many   humans don’t have access to clean water or safe  sanitation systems. In Yemen, for instance,   a massive outbreak of cholera began in 2016 during  a Civil War as the sewage system fell apart.   Did Vibrio cholerae cause that disease outbreak?  Well, in some ways, yes, but in other ways,   it was made possible by human violence  and the breakdown of human-built systems.   It’s no coincidence, of course, that cholera  almost exclusively sickens and kills poor   and marginalized people. Infectious disease  affects people unequally because our governments   and societies treat people unequally.  Disease amplifies structural injustice.   We see that historically, when  cholera disproportionately killed   enslaved Americans in the 19th century.

And  we see it today: Here in the United States,   the Covid-19 pandemic is disproportionately  affecting Black Americans, Native Americans,   and other marginalized groups. And we see similar  disparities from Australia to Germany to Brazil.   And so when we think about disease and its  treatment, we must think not just about   drugs and vaccines and medical devices, but also  about humans: Human history, and human choices,   and human-built systems. Medicine can  treat cholera.

But so can sewage systems.   I think it’s important to use this lens  when thinking about this global pandemic,   because Covid-19 is caused by SARS-CoV-2,  but it is perpetuated by human behavior,   human choices, and the functioning or  failure of human built-systems -- from   healthcare to transportation to governance. Medicines to treat the illness and vaccines   to prevent it are tremendously important, but  so are other interventions we may not be used   to thinking of as medicine--like for instance  wearing a mask in public, washing our hands,   and keeping physical distance between people. Just  as Covid spreads through our behavioral choices,   it can be prevented by them.

Even if you're  not in a position of systemic power, there is   power to the choices you make as an individual. And when we expand our understanding of healthcare   to include human choices, we can see what a  big deal public health really is. When we as   a society build better sanitation systems, cholera  disappears.

When we as a society use less tobacco,   cancer rates drop. And when we as a society keep  distance when possible and wear a mask in public,   Covid-19 infections decline, and fewer  people are hospitalized, and fewer die.   Complexly has other great channels like Healthcare  Triage with Dr. Aaron Carroll and SciShow that are   providing more in-depth updates on COVID-19.

But  this is Crash Course, so we will stick to our   brand with some widely applicable, evidence-based  public health advice that we put together   with the help of our friends at Operation  Outbreak and the Sabeti Lab at Harvard.   One of the greatest challenges of Covid-19  is that people who’ve been infected with   the virus but don’t show symptoms, or have  not yet developed symptoms, can still spread   the virus. Communities are blind-sided  by this asymptomatic spread since people   don’t know they are transmitting the virus. Recent research tells us that asymptomatic spread   drives much of the disease is common and can cause  super-spreading events, potentially infecting   many hundreds of people at once.

This  happened at a biotech conference in February,   where scientists and researchers from all  over the world congregated in Boston.   While they didn’t know it at the time, at least  one of the attendees was carrying COVID-19,   which they spread around the conference. Later on,  scientists were able to use genome sequencing on   the virus to link this one conference outbreak  to infections in tens of thousands of people.   Since the SARS-CoV-2 virus is primarily spread  through respiratory droplets splattering from   one person to another, anything we can do to  prevent that reduces the risk of transmission.   This means wearing a mask to physically  block droplets from your mouth and nose,   physically distancing to reduce the amount  of people who are exposed to your droplets,   and washing your hands with soap to get rid of  any infectious stuff that you may have touched.   You might have heard of these things in  the context of "flattening the curve,"   which is a way to say that slowing the  spread of infection will help us avoid   overloading our medical clinics  and hospitals with sick people.   An overload of Covid patients decreases the  overall quality of healthcare and can mean   in some cases that people don’t get care at all,  which affects people infected with Covid-19 /and/   anyone else who requires a treatment, access to a  doctor, a hospital bed, or any number of medical   resources. More rapid spread generally means  that our communities suffer greater losses.   Due to the great variety of life circumstances,  there’s no one-size-fits-all Covid-19 protection   advice.

Some folks have a job that requires  them to be in the same room as other people,   or they don't have access to clean  protective equipment, or they have   to take care of an older family member. It's possible that all three of these things   (and more) are true for people involved in  teaching and learning right now. So if you’re not   in that position, you can help people who are by  minimizing the risk of spread in your community   through physical distancing, wearing a  face covering, and washing your hands.   There’s another important public health strategy  for limiting the spread of Covid-19: contact   tracing.

By keeping track of who we’ve come into  contact with, we can track a spreading infection   through communities, and intervene to stop it.  This can be an extremely effective strategy.   It was critical in the control of the 2003 SARS  outbreak and the 2014 outbreak of ebola and will   be particularly important in controlling Covid  because the virus can spread without symptoms.   For contact tracing to work effectively, we  need quick test results--something that has   been a problem in many communities. In lieu of  that, we may need to have difficult conversations   with each other, like for instance, texting a  friend and saying, “Hey, I’ve been coughing,   sniffling, feverish, having trouble breathing,  unable to taste or smell, and/or nauseated. I   haven’t yet gotten my test results, but since we  hung out in the last two weeks and I’m afraid I   may have Covid, you should probably get tested  and consider self-isolating.” But like put more   emojis in your text to make it feel human, or  whatever people do now in their text messages.   It may be uncomfortable, but it’s important.  One sick person notifying their friends can save   many lives by shutting down a potential  path of virus spread.

Of course admitting   to potentially spreading a global pandemic  to a close friend is terrifying! Asking your   close friend if they might be spreading a  global pandemic to you is possibly even more   terrifying! But having these conversations  is the "public" part of public health,   and we need to make choices these  days with bravery and empathy.   Plus, all these things we're learning  now can help us improve global health   in this pandemic and in the future.

We are  developing radically new diagnostic testing   and disease tracking technologies, and the  World Health Organization is tracking over   170 potential vaccines in development right now,  some of which are in Stage-3 human trials.   A vaccine would prepare our immune  systems to fight off this virus so   they aren't completely taken by surprise  and devastated by illness. It will likely   not be a magic bullet to end the pandemic, but  instead another tool we use to control it.   Eventually, we'll be able to talk about  COVID-19 as a "thing that happened and   is under control" instead of "a thing that is  happening." When you are living amid history,   it is very difficult to make conclusions about it.  We don’t know how we will look back on this time,   but we do know that 1. This will end, and 2.

Our  choices matter, and can help it to end sooner.   Here at Crash Course, we hear every day how hard  it is for students, teachers, and parents to   navigate education right now. We hear that it’s  hard on physical health, and on mental health.   Experiences that used to be a given--that you  will walk in familiar hallways, hug your friends,   play sports with your teammates, sit in  lecture halls, or eat lunch in the cafeteria   while surreptitiously watching a Crash Course  video to cram for a test--may be gone.   Maybe you’re also living with  other, even more profound losses.   All those losses are real, and I’m sorry. This pandemic is also a threat to physical   health, and to mental health--something I’ve  experienced and I know many of you have, too.   Check in with friends and family.

Reach out for  help when you need it. And remember, the active   choices you make to limit the transmission of the  virus are a gift to yourself, and also to others.   But we must keep learning. Let us find ways to go  on learning about science and history--trying to   better understand the universe and our place  in it.

Let us go on learning about disease   and how to treat it--not just with medicine,  but also by fighting for a more equitable world   where disease no longer disproportionately burdens  the most vulnerable. Let us go on learning about   mathematics, so that we can understand  the implications of exponential growth   before we have to live with those implications. Our species has been around for over 200,000   years, and just a thousand years ago--less  than one half of one percent of our history--we   didn’t know what caused disease pandemics.

We  didn’t know that lead paint was dangerous. Few   if any people knew that the Earth revolved around  the Sun. But because we are able to accumulate and   pass down so much knowledge through generations,  we now know all of that, and so much more.   The people of the past worked together to learn,  and then handed down to us what they knew,   as now we will work together to learn more, in  the hopes that we can help the humans of the   future.

Learning together across vast expanses  of time and space is the human superpower.   To help you use that superpower, Crash Course  is hoping to develop a series on public health,   because--you know--we need to learn more about  illness and the factors that shape human health.   And more generally, we hope that our videos here  can be one tool among many to help keep people   learning and fight for a more equitable world. I don’t want to minimize the challenges of this   moment. They are immense.

This sucks. But I  really believe that even in these upended times,   we must find ways to go on learning the  best way humans learn: Together.   So thanks for being here with us, and  remember, your choices matter, you matter.