30 days challenge The outbreak of influenza began in 1918, during the last months of World War I, and historians today believe that war may have played a part in the spread of the virus. Soldiers on the Western Front who lived in straits, dirt, and dampness fell ill. The main and direct reason for this was the lowering of the soldiers' immune system due to malnutrition. Their disease, known as "la grippe" (meaning flu), was contagious and spread among the army. Within three days of illness, many soldiers recovered, but not all survived.In the summer of 1918, as the battalion returned home for leave, they brought home the unknown virus that had made them sick. The virus spread in the cities and villages of the country where the soldiers live. The recovery process of many sufferers, both soldiers and civilians, was not rapid. The virus had a greater impact on young people between the ages of 20 and 30 who were previously healthy.