The great killer in Ireland in 1918-19, was not political violence nor the Great War, but the ‘Spanish Flu’.
Where it came from nobody knew. The illness was nicknamed the “Spanish lady” because it was first recorded in Spain. Offended Spaniards dubbed it the “Naples soldier”, and the Japanese called it “American influenza”. Sore throat, headache, fever and black skin proved telltale signs (hence it was also known as "the Black Flu"). The more virulent strain of this pandemic was notable in that it primarily killed healthy young adults often within 24 hours of onset.
Troops sailing home from WWI took the flu into Dublin and Cork. The first recorded outbreak was on USS Dixie off Cobh in May 1918 and by July it had arrived in Dublin. From the ports the disease swept across Ireland in three waves: mild in spring 1918; lethal in autumn 1918; and moderate in early 1919.
The top scientists of the day considered the disease was carried by bacteria and was no more deadly than the Russian Flu of 1889-92. Consequently, the authorities did not make it “notifiable” until the third outbreak in spring 1919. (Only in 1933 was it identified as a virus H1N1A).
While the outbreak of ‘Spanish flu’ in Ireland was probably brought back to Ireland by returning soldiers, the epidemic spread due to the intense political activism (i.e. monster rallies) surrounding the General Election of 1918. In addition, being imprisoned, as several thousand Republican activists were, for longer or shorter periods both in Britain and Ireland was probably the worst place to be. The Republicans’ witness statements are full of mournful accounts of comrades who died of the disease in prison. The victory parade for the Great War in Dublin in early 1919 also helped to spread the disease.