A Closer Look – Opportunity Knocks: When Humankind Opens the Door to Disease
Microorganisms are opportunists, constantly seeking circumstances that will allow them to survive. For those that can parasitize human beings, this means infecting susceptible people and moving through a population, one person to the next. The more susceptible hosts in a population, the longer pathogens stick around. Gaps in a community’s collective defenses are a gift to these survivalists.
As the vessels of choice for some of these disease-causing agents, we often focus on the technologies that we have developed against them. Technologies aside, however, human behavior and societal circumstances also play a critical role in whether or how long a microorganism can circulate in a particular community. Below, we discuss three instructive examples of social or societal factors worsening the spread of an infectious disease.
The 1918 Influenza Pandemic and “The Great War”
One of the most well-known disease outbreaks was the 1918 influenza pandemic, known as the “mother of all pandemics.” At the time, healthcare professionals and scientists still didn’t know what kind of organism caused “the flu;” it would be another decade before the virus itself was discovered. In the absence of good understanding of or treatments for the virus, the 1918 flu was poised to run rampant through vulnerable populations. At the same time, another massive world event was endangering the global population: “The Great War,” now more commonly known as World War I. The never-before-seen circumstances of World War I provided influenza virus just the opportunity it needed to explode.
As soldiers from around the world mobilized, the virus seized on the convenient transport in its search for susceptible hosts. Soldiers carried the virus from camp to camp within countries and across oceans, enabling the virus to spread among their allies and enemies alike. The virus also took advantage of opportunities outside of military movements, seizing on local events aimed at supporting the war effort, such as the Liberty Loan Parade held in Philadelphia. According to accounts, the parade was held as scheduled despite rampant influenza infection rates at nearby military encampments. The result was a devastating spread of the disease throughout the city. Philadelphia was not alone; the virus took advantage of opportunities at gatherings worldwide.
In addition to the convenient hitchhiking that enabled the virus to travel far and wide, the war effort had another, perhaps less intuitive, impact on the pandemic. Efforts to maintain troop morale and hide any signs of vulnerability from the enemy caused countries to limit or “finesse” public sentiment about the impact that the virus was having on their own communities and troops. For example, public legislation, such as the U.S. Sedition Act of 1918, was put in place. This U.S. policy rendered any negative or potentially critical discussion of the U.S. government or World War I a federally prosecutable crime. Other countries did the same. As a result, truthful and accurate reporting on the nature of the burgeoning influenza pandemic was stifled across the western world. As countries limited information, the public was unprepared to handle the surge of illness in their communities. In a twist of irony, Spain (as one of the few neutral parties in Europe) did not censor reports of its influenza burden. The relative freedom of the Spanish press to report on the illness spreading within its borders led to incorrect assumptions that the virus originated in Spain. The endurance of that falsehood is apparent even today as people continue to refer to the “Spanish Flu” when discussing the 1918 influenza pandemic despite the certainty that the virus originated elsewhere.
Today, with the names of the estimated 50 to 100 million people lost to the 1918 influenza scourge mostly forgotten, it is difficult to say how many of them may have been spared had the timing of the war and the pandemic not been coincident. To gain advantages in the human-on-human war, the importance and potential impact of the global microbe-on-human war were dismissed. When all was said and done, more people died of influenza during the pandemic than perished on the battlefields of World War I.
The Effort to Eradicate Polio
The 1918 influenza pandemic hit when our understanding of and ability to combat the deadly virus was still limited. As time moved forward, we developed countless strategies to fight not only influenza, but other dangerous pathogens. For example, vaccination against smallpox was so successful that we eliminated it entirely from the planet. No one has contracted smallpox since 1980. The elimination of a pathogen from the entire world is known as eradication. Achieved once, eradication became the goal for another destructive virus — poliovirus.
Killing or disabling hundreds of thousands of children a year in the mid-20th century, polio was a global public health crisis. With polio vaccines in hand, scientists and public health officials set their sights on eradicating polio. It seemed like an easy target. First, unlike influenza, which infects people as well as many types of animals, polio only infects people, so eliminating it ”simply” required stopping all person-to-person transmission. Second, the virus can’t survive for long outside of a human being, so it won’t easily be reintroduced to humans if transmission is stopped. Third, we have effective vaccines, making it possible to limit the number of susceptible people in communities. Despite these biological bonuses and technological advances, eradication has yet to be achieved. We are close, but in 2024, natural poliovirus infection has yet to be eliminated in two countries: Afghanistan and Pakistan.
Why haven’t we been able to stop the spread of poliovirus in those two countries? Successfully vaccinating the world’s population against a pathogen like polio requires getting vaccines to the places they are needed, recruiting healthcare workers to administer them, and convincing the local population to receive them. Unfortunately, vaccination campaigns aimed at local populations in portions of Afghanistan and Pakistan have hit several obstacles.
The locales where polio remains endemic tend to be remote and geographically isolated, resulting in difficulties merely accessing some populations. Additionally, many of the remaining areas where polio remains entrenched are also areas that have been witness to consistent, violent conflict during the past half-century. As a result, access to certain high-need areas has often been denied to healthcare workers for their own safety. Furthermore, the military invasion of Afghanistan by the United States led to distrust of western countries, which extended to vaccines originating primarily from the same countries. Worsening matters, in 2011 the U.S. Central Intelligence Agency (CIA) used the excuse of a vaccination campaign as cover for covert military action in Pakistan. This revelation devastated local trust in vaccination — the effects of which can still be felt today. Once again, conflict between humans left the door open for a pathogen to continue circulating.
The COVID-19 Pandemic
Whereas the 1918 influenza pandemic was characterized by the events of a global war and polio eradication by weaponization of technology-dissemination efforts, our shared experience during the COVID-19 pandemic demonstrates yet another example of how people’s behavior can affect the opportunities for a microorganism. While the same strain of coronavirus started sweeping the planet in 2019, each nation reacted differently. The policies adopted (or not) in response to the pandemic greatly influenced SARS-CoV-2’s opportunity to spread.
During the height of the pandemic, many nations that reported lower increases in their annual death rates were the same ones that instituted broad-reaching and stringent containment measures. Countries such as New Zealand, Singapore, and Taiwan implemented strict case monitoring, mandatory lockdowns and mask mandates; these countries also recorded lower numbers of COVID-19-related deaths. Other countries, including the United States, implemented fewer public health containment measures and subsequently recorded higher death rates. While it is difficult to account for all of the factors that influenced the variability in impact of COVID-19 from country to country (e.g., healthcare infrastructure, cultural differences and poverty rates), generally speaking, those with stricter containment measures suffered fewer deaths due to COVID-19.
Public policies often reflect the values and expectations of the population they affect. Their effectiveness is informed by individual adherence to and enforcement of these policies. In the case of COVID-19, the success of mitigation policies and public mandates was dependent on implementation timelines, individual adherence, and local enforcement. When citizens (whether voluntarily or by legal requirement) followed public health guidelines, the virus struggled to spread. However, many governments grappled with consistent policy implementation and enforcement as well as communication strategies that effectively convinced large segments of the population to adhere to recommendations and policies. In the United States, the science and reasoning behind these life-saving measures was viewed through lenses focused on individual values and social norms. For some, those lenses included skepticism, fear, historical inequities, personal freedom, resistance to authority, and distrust of government and science.
While large portions of the U.S. population adhered to policies and used the tools at our disposal, such as masks and vaccines, many opted out. Indeed, some state governments “opted out” for their entire populace, bucking federal guidance and resulting in an even more welcoming environment for the virus as people moved around, behaving as if a pandemic was not occurring. SARS-CoV-2 capitalized on these opportunities. Like the 1918 influenza pandemic and polio eradication efforts, societal factors affected the ability of SARS-Co-V-2 to spread. But, unlike those examples, the COVID-19 pandemic demonstrated how social norms and values in place at a moment in time can change the course of history. In the 21st century, the human-to-human conflict was not one of physical war but rather one of intellect.
In Summary
Our social and political circumstances will change over time, but pathogens will remain opportunists, ready to spread anytime they are given the chance. And, although we can leverage human-made technologies, like vaccines, tests, and treatments, we will always be at the mercy of the social and political context in which such technologies can be deployed. Influenza, polio and SARS-CoV-2 viruses collectively killed millions — some of whom died simply because of the moment in time during which these events occurred. What are their names? How would history be different? We will never know.
Related resources
The Great Influenza: The Story of the Deadliest Pandemic in History (book)
See the Spread: Watch how the influenza pandemic spread across Philadelphia (animation)
Global polio eradication effort struggles with the end game (interview)
Polio eradication: Reaching every child in Afghanistan with polio vaccines (article)
In photos: how vaccines reach the most remote places on earth (article)