The first reported case of Covid-19 originated in Wuhan, China, on December 31, 2019.

The increased speed and size of the merchant ships of the late 19th century allowed the spread in Puerto Rico of a little-remembered pandemic, the bubonic plague.

In 1918, in the midst of a massive mobilization of troops in World War I, an epidemic of influenza AH1N1 began to spread and led to a brief but lethal pandemic.