How Does a Pandemic Start and Why Does it Spread so Quickly?
We’re now months into the COVID-19 pandemic, with months to go until we’re out of it. It seems like only a few weeks ago the virus was contained to China. Then it spread to Italy. Then Spain. Then, as if overnight, the U.S. eclipsed 100,000 cases. Such is the power of a global pandemic. But how does an infectious disease become so widespread so fast? And why can’t we seem to flatten the curve fast enough?
Understanding the roots of a pandemic
When COVID-19 first emerged, many terms were used to discuss its impact on global health. First it was called a disease, then an outbreak, then an epidemic, then a pandemic. Although many have conflated these terms, they mean different things.
An epidemic is a disease that affects a large number of people within a region. When COVID-19 began spreading rapidly through Wuhan, China, it was an epidemic. Once it spread to other areas of China, those new segments of disease were called outbreaks. Eventually, COVID-19 spread to other countries, including Italy, the United Kingdom, and the United States. By mid-March 2020, it was a pandemic — a disease spread over multiple countries and continents.
But how does a pandemic begin? To understand this, researchers must trace the disease back to the original patient (patient zero) and examine the disease’s spread patterns. Although we might not always find patient zero, at a minimum, we can understand where the disease came from.
When COVID-19 was first identified in China, it wasn’t certain what exactly it was or where it came from. Experts still can’t pinpoint patient zero. However, by examining the epidemiology, they now believe that the disease is zoonotic, or of animal origin. After its transmission from an animal to patient zero (or multiple patients), the disease was spread through human contact.
Passing from person to person within Wuhan, then throughout China, then overseas to new countries, COVID-19 crept across the globe.
High viral load contributes to rapid spread
Not all epidemics end up becoming pandemics. The rate at which a disease spreads — whether throughout a region or overseas — has a lot to do with how it spreads and how infectious it is. Unfortunately, in the case of COVID-19, high viral loads made infected people more contagious, leading to a global outbreak.
After the initial patients became infected, experts believe COVID-19 spread via close contact with other people and respiratory droplets. It’s now understood that people can have high viral loads and spread the virus before showing symptoms of illness.
This caused exponential spread — particularly in populated areas — since one person could infect five others, who each went on to infect five more, all without realizing they were exposed or infected. Additionally, people who were exposed may have been traveling internationally and brought the disease with them as they flew to other countries.
How can the pandemic be stopped?
Initially, those who were exposed to or infected with the virus were asked to self-quarantine to prevent the spread. Now, because infected people may not show symptoms, many states and countries have enacted shelter-in-place orders and encouraged social distancing to keep people from interacting with one another.
In healthcare settings, person-to-person contact is required, which is why personal protective equipment (PPE) is so crucial for protecting nurses and doctors. PPE minimizes providers’ exposure to infected respiratory droplets, reducing their risk of illness. And for people at home, washing hands thoroughly can help remove viral particles to reduce the risk of transmission. It is only through these protective measures that we can #FlattenTheCurve and eradicate the virus.