Since the dawn of humanity, our species has contended with an invisible adversary: the infectious disease. Before modern medicine, it brought down entire civilizations and was by far the leading cause of death. Because of infectious disease, simple cuts could kill and few lived to adulthood.
Source: CDC Public Health Image Library. Image by Jennifer Oosthuizen, 2019.
Then came vaccines.
Though ideas like vaccination have existed for centuries, the first vaccine is generally associated with an English doctor named Edward Jenner. His story began with a simple observation of heightened immunity to Smallpox—a disease as contagious as COVID but many times deadlier—among milkmaids. Though the virus that caused Smallpox had yet to be isolated—the first viruses weren't until the late 19th century—Jenner theorized that immunity to Smallpox could be acquired through exposure to a similar disease. Indeed, it turned out that the milkmaids frequently contracted the Smallpox-related Cowpox virus from animals they worked with, and that material from their Cowpox sores could be used as a vaccine. In May of 1796, an 8-year-old boy named James Phipps received the Jenner vaccine and became immune to Smallpox, marking a turning point in the fight against infectious disease.
In the following 150 years, several gains rivaling Jenner's discovery were made. In 1877, Louis Pasteur coined germ theory, allowing scientists to understand that the true cause of most infections were tiny microorganisms that replicated in their hosts. 2 years later, Pasteur tested a vaccine against Cholera in chickens, which had caused 4 pandemics and millions of deaths up to that point. By the end of the 19th century, vaccines would be developed against Rabies, Cholera, and Typhoid.
However, modern medicine had yet to fully mature and not all diseases could be countered. One particularly large lethal reminder of this fact took place in 1918.
Though the most famous historical event of that year was World War I, 1918 was also the year the Spanish flu—an ancestor of the current seasonal flu—killed up to 5 times as many as the war in half the time. We will never know the true death toll of that pandemic, but an estimated 17.4-100 million people (1-5% of the world population) died. Even worse, most deaths occurred in a few weeks during the fall of 1918. This was totally unlike WW1 deaths, which were spread out over 4 years.
Ironically, the Spanish flu was quickly forgotten despite killing more per capita than WWI and possibly WWII, a phenomenon attributed by some to its short duration or the sheer trauma and incomprehensibility of its scale.
The deadliest disasters in human history have been caused by infectious disease pandemics. Sources
By 1928, a new golden age of medicine began with Alexander Fleming's accidental discovery of Penicillin. After going on vacation and leaving out a Petri dish teeming with Staphylococcus bacteria, Fleming returned to find mold growing against the bacteria. He quickly found that the mold was producing bacteria-killing chemicals, leading to the discovery of the Penicillin antibiotic.
After 1928, more than 100 antibiotics were discovered, countering a huge range of leading infections. Through their use from ordinary hospital wards to the battlefields of WWII, these drugs likely saved hundreds of millions of lives. Simultaneously, other advances were made. New technologies like ventilators and electron microscopes, as well as more simple advances like improved sanitation, all helped bring down the burden of infectious disease.
The results were clear: in the United States, Polio, Measles, and Malaria were wiped out. Globally, the Smallpox virus that inspired Edward Jenner was eradicated after killing almost half a billion people in the 20th century. Since the last natural Smallpox infection in Somalia in 1977, the virus has only existed in a handful of laboratories worldwide, marking one of the greatest health victories in human history.
The eradication of Smallpox is widely considering one of the greatest health victories in history. Source: Statista
Luckily, humanity didn't stop at Smallpox. Other major infectious diseases like Polio and Measles were eradicated in many countries and heavily reduced in most. Even the most persistent diseases like Tuberculosis began to cause less and less mortality each year. Before long, infectious diseases disappeared as leading causes of death in developed nations altogether.
There were hiccups along the way, of course. From 1957 to 1968, new pathogens emerged, sparking three pandemics—one of Cholera and two of Influenza—killing millions worldwide. Still, by the late 1960s, Nobel Peace Prize Winner Frank MacFarlane Burnet was confident enough to declare that infection had been eliminated “as a significant factor in social life,” echoing widespread sentiments in medicine and health.
He was wrong.
In July of 1981, the US Centers for Disease Control and Prevention reported on an unusual rise in Kaposi's Sarcoma, a rare form of cancer, in several gay men in San Francisco. It would take until 1983 for a new virus named HIV to be discovered as the cause. By the time the disease was recognized as a global health threat, millions were infected. At the height of the AIDS pandemic, life expectancy in Sub-Saharan Africa, the epicenter of the outbreak, fell by almost 20 years. Even with the introduction of antiretroviral drugs that transformed HIV from a universally fatal disease to a survivable one, the pandemic continued. Part of this is due to widespread health inequality, with millions of HIV victims in low-income countries still unable to access treatment.
To date, the HIV pandemic has killed more than 40 million worldwide. A million more are infected every year, and over half a million die.
HIV/AIDS has had devastating consequences on a global scale, infecting close to a fifth of the population in some areas. Source: OurWorldInData
In 1918, we weren't ready and the Spanish Flu killed up to 100 million people. In 1981, we still weren’t ready for HIV/AIDS.
In the years since 1981, the world has experienced several international health emergencies: Ebola, SARS, Swine Flu, and Zika. Each time, shortfall after shortfall in global health preparedness was exposed. Warnings were issued, promises made, and plans drafted, but there never was a true commitment to preparing for the next big infectious disease.
Enter COVID-19. In 3 months, it swept the globe. Despite the unparalleled speed with which vaccines and drugs were developed and the near-total shutdown of global society, the virus still infected nearly every person on the planet. As with the Spanish flu, we will never know the true toll of COVID-19, though its likely far higher than the 7 million deaths that have been reported (excess deaths, a key measure of true mortality from larger disasters, are estimated to be in the range of 20-30 million). Additionally, with an economic cost exceeding 20 trillion dollars, this single infectious disease caused 5 times more economic damage than every climate-related disaster in the last 50 years combined.
Pandemics caused by entirely new diseases aside, there is another problem: antimicrobial resistance. The very drugs that prevent countless deaths by infectious disease are vulnerable to disease evolution. Without careful stewardship of these drugs, there can be lethal consequences—in fact, some of those consequences are already here.
The emergence of drug-resistant bacteria killed millions of people last year, accelerated by our careless and excessive use of antibiotics. At this rate, the death toll from antimicrobial resistance is expected to exceed 10 million a year by 2050.
Infectious diseases continue to kill millions worldwide. Source
Indeed, advances in medicine have massively reduced global mortality from infectious diseases, but they have not been eliminated as a "significant factor in social life." Even without counting the COVID-19 pandemic, more than 10 million people are dying every year from the top 11 infectious diseases. Tragically, many of these deaths can be prevented by vaccination a wide range of available treatment options. The problem is accessibility: such "luxuries" are rarely afforded to those in low-income countries.
As a result, the war on infectious disease continues on multiple fronts. On one front, we face emerging threats like new pandemics and drug-resistant superbugs, which are proliferating more and more in our increasingly interconnected world. On another, global health inequity means that more familiar infectious diseases, which are entirely preventable and largely eradicated in wealthy countries that have access to the right tools, continue to kills tens of millions of people worldwide.
Clearly, even setting drug-resistant superbugs and unpredictable pandemics aside, we still have much work to do.
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