The Spanish influenza pandemic in the years 1918–1920 was the largest and most tragic pandemic of infectious disease in human history. Deciphering the structure of the virus (including the determination of complete genome sequence) of this pandemic and the phylogenetic analysis and explanation of its virulence became possible thanks to molecular genetic analysis of the virus isolated from the fixed and frozen lung tissue of influenza victims who died in 1918 and were buried frozen in Alaska and Spitsbergen. Epidemiological data from the course of this pandemic in Poland have not been previously published. For analysis, we used source materials such as clinical studies and case reports of doctors fighting against the pandemic and registries of influenza cases in units of the Polish Army and military hospitals. Clinically, the pandemic of 1918 was characterized by the same symptoms and course as influenza in other years. Pathologically, the disease was similar to the other pandemic, in that the destruction was mostly limited to the respiratory tract. The “Spanish” influenza pandemic of 1918–1920 took place in Poland in 3 epidemic waves. The peaks of morbidity and mortality occurred in the capital, Warsaw, in December 1918 and in December 1919 to January 1920. It is estimated that throughout the pandemic period of 1918–1920 in Poland, 200 000 to 300 000 people died.

Keywords: Epidemiological Monitoring, Influenza Pandemic, 1918-1919, Poland, Public Health