Background From 1918 to 1920, the largest influenza A virus (IAV) pandemic known to date spread globally causing between 20 to 100 million deaths. Historical records have captured critical aspects of the disease dynamics, such as the occurrence and severity of the pandemic waves. Yet, other important pieces of information such as the mutations that allowed the virus to adapt to its new host can only be obtained from IAV genomes. The analysis of specimens collected during the pandemic and stil...
