http://www.sciencemag.org/news/2021/05/human-tissue-preserved-world-war-i-yields-new-clues-about-1918-pandemic

A gymnasium in Boden, Sweden, is filled with pandemic influenza patients in 1918. Researchers have pieced together a full genetic sequence of the flu virus circulating in Europe at the time.

On 27 June 1918, two young German soldiers—one age 18, the other 17—died in Berlin from a new influenza strain that had emerged earlier that year. Their lungs ended up in the collection of the Berlin Museum of Medical History, where they rested, fixed in formalin, for 100 years. Now, researchers have managed to sequence large parts of the virus that infected the two men, giving a glimpse into the early days of the most devastating pandemic of the 20th century. The partial genomes hold some tantalizing clues that the infamous flu strain may have adapted to humans between the pandemic’s first and second waves.