History’s deadliest teacher: What three deadly pandemics taught us
Are pandemics the best teachers in history?1
Pandemics suck. No one’s rooting for them. Zero out of ten. Would not recommend. Still… these world-altering events taught humanity a lot. The horrific plagues of our past also gave us weapons against them and future plagues.
The Black Death gave us quarantines. Cholera outbreaks taught us the importance of water and sewage treatment. COVID-19 helped us perfect wastewater-based epidemiology (how we get the scoop from poop). Two scourges—malaria and polio—are still teaching us lessons that scientists around the world are using to eradicate those diseases. Pandemics have killed hundreds of millions of people across our long history. Yet, these tragedies have taught us to fight back. Childhood mortality has collapsed. In 1800, with child mortality around 40%, many parents knew what it felt like to lose a child. Today, at under 4%, that experience is the exception rather than the rule.
The history of human settlement, expansion, and global connection is also the history of infectious disease. As we’ve swept across the Earth, so have our deadliest adversaries and greatest teachers. Let’s examine three of history’s worst diseases and the lessons they taught us.
Smallpox: Disease is not inevitable
For over 3,000 years, smallpox was a mirror of humanity. It rose with us as we built cities. It traveled with us as we built empires and trade routes linking the world. Evidence of smallpox lesions has been found on ancient Egyptian mummies. Pericles of Athens led his people in a war against Sparta, but it wasn’t a Laconian spear that felled the great statesman. Some historians believe that smallpox was behind the Plague of Athens in 430 BCE, which killed Pericles and one third of his city-state, undermining the Athenian war machine. In 165 CE, the Antonine Plague decimated Roman legions, forcing Marcus Aurelius to hire German mercenaries, and ushering in the beginning of the end of the Pax Romana. By far, the deadliest smallpox outbreaks were during the Great Dying, in which European colonizers brought smallpox and several other diseases to the Americas, killing 50 to 90% of the Indigenous American population. Smallpox has clung to us like a leech, quietly steering the course of human history.
We can trace its oozing trail through our history because it’s one of the best-documented diseases. As it moved, affected communities learned ways to fight back. It’s a millennia-long story that ended in 1980.
In tenth-century Asia and a bit later in Africa, people were experimenting with early forms of inoculation. By scraping a smallpox sore or collecting the fluid from an infected lesion, healthy individuals could inoculate themselves if they inhaled those pustule bits or added them to a cut on the skin. Inoculated people generally had milder cases of the disease and were immune to later infections, although the process required a willingness to stomach coming into contact with someone else’s pustule.
In 1796, English physician Edward Jenner created the first vaccine against smallpox using cowpox, thus laying the foundation for the plethora of vaccines the world relies on today. But smallpox didn’t disappear. In the twentieth century alone, smallpox killed over 300 million people—more than both world wars and the 1918 influenza pandemic combined.
From 1967 to 1980, the international community managed to leverage new innovations in the first-ever disease eradication campaign. On May 8, 1980, smallpox was officially eradicated. This success depended on international cooperation to surveil and contain the disease and to strategically vaccinate individuals on a global scale. The innovation of a freeze-dried, heat-stable vaccine made it much easier to transport it to tropical regions, and new bifurcated needles were “inexpensive, easy to use, and required only a quarter of the vaccine dose.”2 Humanity’s old foe and terrible teacher was gone.
The Spanish Flu: Communication is key
Smallpox taught humanity about the effectiveness of vaccines. At the end of the First World War, the influenza pandemic of 1918—often called the Spanish Flu—taught lessons about communication with the public and across borders.
First, the Spanish Flu was not Spanish in origin. So, we’re not off to a great start communication-wise.
The H1N1 influenza A strain that appeared in 1918 is the ancestor of all subsequent influenza A outbreaks. The worst cases of this pandemic hit people between the ages of 20 and 40, likely due to the confined living quarters and the global transport of military personnel during World War I. As the war was ending, military transports continued to move supplies and troops around the world, spreading the virus fast and far. By the end of the pandemic, over 50 million people had died, mainly as a result of secondary bacterial pneumonia infections.
The flu taught us some hard lessons about communication, the first of which relates to its name. This pandemic probably started at a military training camp. Maybe in Kansas. But the United States and its allies were at war, and strict censorship meant that they hid outbreaks. Neutral Spain, by contrast, freely shared information and reported cases. And the world thanked them by naming the pandemic after them. Nice.
This was serious stuff. Censoring the severity and locations of outbreaks exacerbated the spread of the disease. In 1918, we didn’t have the medical arsenal we have today. There were no influenza vaccines, no antiviral drugs, and no antibiotics. Public health measures were our best hope. Governments that quickly promoted social distancing and contact tracing, banned large gatherings, closed schools and churches, and put up educational flyers encouraging people to mask up and to stop coughing openly and spitting in the street fared better than those who waited. Some cities eased restrictions too early and faced new waves of death.
Governments eventually learned their lessons. After 1918, Canada established a national Department of Health to coordinate disease response. New US laws regulated cramped tenement housing. Soviet Russia established the world’s first state-funded, centralized healthcare system. And in 1921, the League of Nations founded its Health Organization, a precursor to the UN’s World Health Organization. The League used its neutral status to build trust and discourage political censorship, helping to ensure governmental transparency about disease outbreaks.
The AIDS pandemic: We’re in this together
In 1981, a new, baffling pandemic emerged. Presenting first as pneumonia infections and cancers that were primarily impacting previously healthy gay men, by September 1982, the CDC defined the disease as acquired immune deficiency syndrome (AIDS). That same month, two US congressmen introduced legislation to fund AIDS research, but Congress waited a year to pass it and allocate funding. It would take another year before the cause of AIDS was identified as human immunodeficiency virus (HIV). Since then, HIV/AIDS has impacted millions of people, with about 44 million deaths worldwide.
When AIDS cases began to multiply, many believed that the disease was confined to the gay community and intravenous drug users. As a result, it was treated by some people and governments with callous disregard. Infected people were met with stigma and isolation. Governments passed punitive laws and migration restrictions. Public panic, political inaction, and medical ignorance fueled widespread discrimination. Yet, within the first few years, the number of cases in other populations swelled. With so much unknown about transmission methods and due to fear of discrimination, many of those infected refrained from getting tested and seeking medical treatment, worsening the spread.
Here’s what these failures taught us: In the face of prejudice and political apathy, grassroots activism and global solidarity can change the course of science. In the absence of governmental leadership, groups like ACT UP used civil disobedience to push for faster drug approvals and force governments to act. The AIDS pandemic also illustrated that it’s in the interest of wealthy nations to share resources to combat infectious disease. Initiatives like the 2003 President's Emergency Plan for AIDS Relief (PEPFAR) have helped prevent infections and saved tens of millions of lives. By investing in global public health, wealthy nations like the US are also protecting their own people.
In recent decades, there have been many triumphs in combating HIV/AIDS. New treatments mean the disease is no longer a death sentence. Preventive advances have curtailed new infections, and vaccines are in medical trials. Still, there are about 41 million people currently living with HIV. Each year, about 570,000 people die from AIDS-related illnesses.
More recently, it appears that lessons have been forgotten. In 2025, the US shut down USAID, and several other wealthy nations have reduced foreign aid for disease prevention. Some studies have predicted these cuts could cause up to 10 million new HIV infections and as many as 2.9 million HIV-related deaths by 2030. Without access to lifesaving treatments and education about the disease, millions will suffer, especially in underserved communities and developing nations.
Are we ready for the next pandemic?
The answer to this question is complicated. We’ve learned a great deal from pandemics of the past. We’ve developed new tools, such as vaccines, and we’ve established public health standards and improved global cooperation and communication. Vaccine development now takes a fraction of the time it once did and is more effective than ever. Relatively inexpensive at-home testing now gives people accessibility without having to go to a clinic. Hospitals and public health boards have better ways to contact trace and report on the spread of disease including wastewater testing, which can detect viruses before there’s an outbreak.
Still, pandemics are imperfect teachers. As students, humanity often forgets the lessons of the past. We repeat mistakes as the memories of lessons fade. And, from time to time, a pandemic decides that it’s time for the class to review.
Global health funding is collapsing at a historic rate. From 2023 to 2025, international health aid fell 30 to 40%, while development assistance suffered its largest annual cut on record in 2025, plunging more than 23%.
Public distrust has led to new measles outbreaks as parents opt out of giving their children lifesaving vaccines. The wealth divide between rich and poor nations continues to impact access to vaccines and treatments. Conspiracy theories and misinformation about the COVID pandemic, vaccines, and other public health topics flood social media.
So, what can educators do to help our students learn from history’s scariest teacher? First, we can prepare them to recognize and combat the spread of misinformation and disinformation. Students must develop their critical thinking and digital literacy skills. We can teach them the power of claim testing to separate fact from fiction. But you should also flip the script on your students and ask them what they think the next pandemic might teach us. What new lessons do we still need to learn? Are there old lessons we’ve forgotten? What can we do before it’s too late? You’re bound to get some surprising answers. Be sure to share them with other teachers in the OER Project Teaching Community!
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1 Apart from OER Project teachers, of course.
2 D.A. Henderson and Petra Klepac, “Lessons from the Eradication of Smallpox: An Interview with D. A. Henderson,” Philosophical Transactions of the Royal Society of London B: Biological Sciences 368, no. 1623 (August 5, 2013). https://doi.org/10.1098/rstb.2013.0113.
Header image, left: An electron micrograph of the virus that caused the 1918 flu. CDC’s Public Health Image Library (PHIL), public domain. Right: "February 1919. U.S. Army at Archangel Front, Russia. Funeral of member of crew of U.S.S. Ascutney. Three members died in Archangel and many were sick with influenza." National Archives, public domain.
About the authors: Bridgette Byrd O’Connor holds a DPhil in history from the University of Oxford and taught the OER Project: Big History course and AP US government and politics for 10 years at the high-school level. She currently writes articles and activities for OER Project: World History and Big History courses. In addition, she has been a freelance writer and editor for the Crash Course World History and US History curricula.
Bennett Sherry holds a PhD in history from the University of Pittsburgh and has undergraduate teaching experience in world history, human rights, and the Middle East. Bennett writes about refugees and international organizations in the twentieth century and is one of the historians working on the OER Project courses.