Illustration of the lung of a patient that died of Spanish flu. Grey areas have become filled with fluid rather than air. The upper lobe (right) is congested and there is a large haemorrhage at centre. It is thought that a severe immune system overreaction, known as a cytokine storm, was responsible for such lung damage, which was often fatal. The 1918 Spanish influenza pandemic, which occurred in several waves between 1918 and 1920, infected one fifth of the world population and killed between 20 and 50 million, more than had been killed in the First World War. The second wave of the pandemic, from August 1918, was much deadlier than the first, with high mortality rates among young healthy adults. Illustration from 'The Pathology of Influenza' by M. C. Winternitz, Isabel M. Wason and Frank P. McNamara (1920). |