COVID-19 and Spanish Flu, the Representative Pandemics of the 21st and 20th Centuries

We are still in the early stage of 21st century and the two pandemics Spanish flu and COVID-19 are the presentative pandemics in 20th and 21st centuries, respectively. The Spanish flu pandemic raged from 1918 to 1920, just after World War I. It was the first influenza pandemic worldwide; since then, humankind has experienced many such pandemics. Spanish flu is caused by a virus. However, since virology was not well established at that time, the new clinical system was needed to cope with "unknown pathogen"; during the pandemic, high infection rates were recorded, but our predecessors managed to somehow tackle the situation. With respect to the ongoing COVID-19 pandemic, both the virus and its genome were clarified quickly. Nonetheless, it has turned out to be quite an intriguing infectious disease, with the high rates in developed countries, such as the US and those in Europe, which have aging societies, and low rates in developing countries such as those in Africa, where the population is largely young. Here, I compared and discuss the two pandemics, COVID-19 and Spanish flu.