This occurred when soldiers returned to the Roman Empire after a war against Parthia and brought a sickness that may have been smallpox. It wiped out over 5 million people in the empire and destroyed army forces. The plague caused instability that led to the end of the Pax Romana, or Roman Peace (the height of the empire's power).

Perhaps the most well-known pandemic in all of history, the Black Death devastated communities from Asia to Europe, wiping out over half of Europe's population. Thousands of cases of the plague are still reported each year, mostly in sub-Sarahan Africa and Madagascar, though cases increased six-fold in Asia during the Vietnam War. However, the plague had unexpected benefits in Europe: labor was harder to find among the living population, so surviving workers were paid more and had better benefits, bringing an end to the tyrannical system of serfdom in Europe.

The American Plagues describe a cluster of diseases brought to the Americas by European explorers, most notably smallpox. An estimated 90% of the native population in the entire Western Hemisphere was wiped out, contributing to the collapse of large civilizations like the Incans and Aztecs.

The earliest cases of the flu were reported in Russia. Because of the modern industrial age, the disease was able to spread all over the globe in just a few months through chains of transport spanning Europe and Asia. About 1 million people were killed worldwide. However, it's not certain what specific virus was responsible; there's speculation that it may have been one of the seven known human coronaviruses.

FDR was famously diagnosed with polio in 1921 when he was 39 years old. Several polio epidemics occurred until the Salk vaccine was invented in 1954.

Despite the name, the Spanish Flu did not originate in Spain. Spain was neutral during WWI and therefore didn't strictly censor press, so the illness was freely documented. This led to people thinking the illness was only in Spain, although 500 million people around the world got it. Some indigenous communities were pushed to the brink of extinction, and the spread of the flu was quickened by the poor wartime conditions.

The strain of H1N1 that caused the pandemic originated in Mexico and infected 1.4 billion people around the globe in a single year. Unlike most viral diseases, there was a disproportionate amount of cases in children and young adults. Nowadays, the vaccine for H1N1 is included in a typical annual flu shot.

The ongoing pandemic is caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) and has caused massive global effects, due to ever-increasing population density, ease of travel, and failing health systems in several countries. As of Dec. 14, 2020, more than 72.3 million cases and 1.61 million deaths have been confirmed. 57 vaccine candidates are currently in clinical research. The UK, Bahrain, UAE, Canada, USA, and Mexico have approved the Pfizer vaccine for emergency use, but people in low-income developing countries may not receive vaccines from leading manufacturers until 2024. The COVAX (COVID-19 Vaccines Global Access) initiative is attempting to combat this.