Infectious disease epidemics – outbreaks of a disease that affect a large percentage of people in a community – and pandemics – widespread, global spread of a disease – have transformed societies around the world throughout history. From old favorites like cholera and the plague to new diseases such as SARS, MERS, Ebola, and COVID-19, biological disasters can devastate economies and disrupt social structures. The rapid pace of globalization, increased travel, and changing climate can make it difficult to contain the spread of infectious diseases that threaten human survival.

The definition of the word epidemic has evolved over time. For Hippocrates, the term epidemios referred to groups of similar syndromes occurring in the same place at the same time and spreading “on the people.” By the early 19th century, when Littre coined the modern definition, the term was referring to outbreaks that spread from person to person, either directly (like some sexually transmitted diseases) or through an item or vector that could pass the disease, such as needles, also called vehicle-borne transmission.

The coronavirus that caused the recent pandemic has now transitioned to endemic status, meaning that it has become a constant presence in a population and is no longer spreading quickly. However, the virus continues to evolve and new strains of the virus may emerge in the future with the potential to cause another pandemic. Vaccination is one way to reduce the likelihood of the next epidemic by decreasing the number of susceptible individuals.