The Black Death, the 1918 Flu Pandemic, and COVID-19 are all examples of catastrophic, world-changing pandemics. While we tend to think of these events as unlikely, the reality is that between 1980 and 2020, at least three diseases emerged that caused global pandemics: COVID-19, the 2009 swine flu, and HIV/AIDS. Disease outbreaks are surprisingly common. Over the past four centuries, the longest stretch of time without a documented outbreak that killed at least 10,000 people was just four years. Despite the frequency of smaller outbreaks, many people born after the 1918 flu lived their entire lives without experiencing a similar world-changing pandemic.
There are several ways to estimate the probability of future pandemics. One approach is to look at history. A team of scientists and engineers who took this approach cataloged all documented epidemics and pandemics between 1600 and 1950. They used this data to graph the likelihood of an outbreak of any size occurring somewhere in the world over a set period of time and to estimate the likelihood that such an outbreak would get large enough to kill a certain percentage of the world’s population. This analysis showed that while huge pandemics are unlikely, they’re not that unlikely. The team estimated that the risk of a COVID-19-level pandemic is about 0.5% per year, and could be as high as 1.4% if new diseases emerge more frequently in the future.
Another way to estimate the likelihood of a future pandemic is to model one from the ground up. For most pandemics to happen, a pathogen, which is a microbe that can cause disease, has to spill over from its normal host by making contact with and infecting a human. Then, the pathogen has to spread widely, crossing international boundaries and infecting lots of people. Many variables determine whether a given spillover event becomes a pandemic. For example, the type of pathogen, how often humans come into close contact with its animal reservoir, existing immunity, and so on. Viruses are prime candidates to cause the next big pandemic. Scientists estimate that there are about 1.7 million as-yet-undiscovered viruses that currently infect mammals and birds and that roughly 40% of these have the potential to spill over and infect humans.
A team of scientists built a model using this information, as well as data about the global population, air travel networks, how people move around in communities, country preparedness levels, and how people might respond to pandemics. The model generated hundreds of thousands of virtual pandemics. The scientists then used this catalog to estimate that the probability of another COVID-19-level pandemic is 2.5 to 3.3% per year. To get a sense of how these risks play out over a lifetime, let’s pick a value roughly in the middle of all these estimates: 2%. Now let’s build what’s called a probability tree diagram to model all possible scenarios. The first branch of the tree represents the first year: there’s a 2% probability of experiencing a COVID-19-level pandemic, which means there’s a 98% probability of not experiencing one. The second branch, the same thing, the Third branch, the same. And so on, 72 more times. There is only one path that results in a fully pandemic-free lifetime: 98%, or 0.98, multiplied by itself 75 times, which comes out to roughly 22%. So the likelihood of living through at least one more COVID-19-level pandemic in the next 75 years is 100 minus 22%, or 78%. 78%!
If we use the most optimistic yearly estimate— 0.5%—the lifetime probability drops to 31%. If we use the most pessimistic one, it jumps to 92%. Even 31% is too high to ignore; even if we get lucky, future generations might not. Also, pandemics are usually random, independent events: so even if the yearly probability of a COVID-19-level pandemic is 1%, we could absolutely get another one in ten years. The good news is we now have tools that make pandemics less destructive. Scientists estimated that early warning systems, contact tracing, social distancing, and other public health measures saved over a million lives in just the first six months of the COVID-19 pandemic in the US, not to mention the millions of lives saved by vaccines. One day, another pandemic will sweep the globe. But we can work to make that day less likely to be tomorrow. We can reduce the risk of spillover events, and we can contain spillovers that do happen so they don’t become full-blown pandemics. Imagine how the future might look if we interacted with the animal world more carefully, and if we had well-funded, open-access global disease monitoring programs, AI-powered contact tracing and isolation measures, universal vaccines, next-generation antiviral drugs, and other tech we haven’t even thought of. It’s in our power to change these probabilities. So, we have a choice: we could do nothing and hope we get lucky. Or we could take the threat seriously enough that it becomes a self-defeating prophecy. Which future would you rather live in?
Research one of the historical pandemics mentioned in the article (The Black Death, the 1918 Flu Pandemic, or COVID-19). Create a presentation that includes the causes, spread, impact, and lessons learned from the pandemic. Present your findings to the class.
Using the probability tree diagram concept discussed in the article, create your own probability tree for a different scenario. For example, calculate the probability of experiencing a major earthquake in your lifetime. Present your tree diagram and explain your calculations to the class.
In groups, use a simple computer simulation tool or software to model the spread of a hypothetical pandemic. Adjust variables such as transmission rate, recovery rate, and public health interventions. Observe and record how these changes affect the spread of the disease. Share your findings with the class.
Participate in a class debate on the effectiveness of various public health measures (e.g., early warning systems, contact tracing, social distancing, vaccines). Use evidence from the article and other sources to support your arguments. Discuss which measures you believe are most crucial in preventing future pandemics.
Write a short story or essay imagining a future pandemic scenario. Incorporate elements discussed in the article, such as spillover events, global disease monitoring programs, and advanced public health measures. Describe how society responds to the pandemic and what lessons are learned. Share your story with the class.
Black Death – A deadly bubonic plague pandemic that occurred in the 14th century, causing widespread death and devastation. – The Black Death decimated the population of Europe, wiping out nearly one-third of its inhabitants.
Flu Pandemic – A global outbreak of a highly contagious influenza virus, resulting in a significant number of cases and deaths worldwide. – The 1918 flu pandemic, also known as the Spanish flu, infected approximately one-third of the world’s population and claimed millions of lives.
COVID-19 – A highly contagious respiratory illness caused by the novel coronavirus, SARS-CoV-2, first identified in Wuhan, China in 2019. – The COVID-19 pandemic has led to widespread lockdowns, economic downturns, and loss of lives across the globe.
Diseases – Abnormal conditions or disorders affecting the body or mind, often characterized by specific symptoms and signs. – There are numerous diseases such as cancer, diabetes, and Alzheimer’s that require extensive research for effective treatments.
Swine Flu – A respiratory disease caused by strains of influenza virus that usually infect pigs, but can also be transmitted to humans. – The swine flu outbreak in 2009 resulted in a global pandemic, with millions of people being infected and thousands losing their lives.
HIV/AIDS – A viral infection caused by the human immunodeficiency virus (HIV), leading to acquired immunodeficiency syndrome (AIDS), which weakens the immune system. – The HIV/AIDS epidemic has had a devastating impact on individuals, families, and communities worldwide.
Disease Outbreaks – Sudden occurrences of a specific disease in a particular geographic area or population, often spreading rapidly. – The recent outbreak of Ebola in West Africa highlighted the importance of rapid response and containment measures to prevent further spread.
Probability – The likelihood or chance of a specific event or outcome occurring, often expressed as a numerical value between 0 and 1. – The probability of rolling a six on a fair six-sided die is 1/6 or approximately 0.167.
Future Pandemics – Potential global outbreaks of infectious diseases that have the potential to cause significant illness, death, and societal disruption. – Scientists and health organizations are actively monitoring and preparing for future pandemics to ensure swift and effective responses.
Modeling a Pandemic – The process of creating mathematical or computational models to simulate the spread and impact of a pandemic, helping to inform public health decisions and interventions. – Researchers are using sophisticated models to predict the trajectory of the COVID-19 pandemic and evaluate the effectiveness of different control strategies.
