Just 10 days before von Economos breakthrough in Vienna, Jean-René Cruchet described 40 cases of "subacute encephalomyelitis" in France.The number of people infected during the ten years of the pandemic is unknown, but it is estimated that more than 1 million people contracted the disease, which directly caused more than 500,000 deaths. Encephalitis lethargica assumed its most virulent form between October 1918 and January 1919. The pandemic disappeared in 1927, as abruptly and mysteriously as it first appeared. The great encephalitis pandemic coincided with the 1918 influenza pandemic, and it is likely that the influenza virus potentiated the effects of the causative agent of the encephalitis or lowered resistance to it in a catastrophic way. Aftermath
Many surviving patients of the 1915–1926 pandemic seemed to make a complete recovery and return to their normal lives. However, the majority of survivors subsequently developed neurological or psychiatric disorders, often after years or decades of seemingly perfect health. Post-encephalitic syndromes varied widely: sometimes they proceeded rapidly, leading to profound disability or death; sometimes very slowly; sometimes they progressed to a certain point and then stayed at this point for years or decades; and sometimes, following their initial onslaught, they remitted and disappeared. Postencephalitic Parkinsonism is perhaps the most widely recognized of such syndromes. Notable cases
Notable cases include:

Muriel "Kit" Richardson (née Hewitt), first wife of actor Sir Ralph Richardson, died of the condition in October 1942, having first shown symptoms in 1927–28.
Between 1750 and 1800, France and Germany experienced minor epidemics of "coma somnolentum" with features of Parkinsonism, including hyperkinetic hiccup, myoclonus, chorea, and tics. Between 1848 and 1882, Paris-based neurologist Jean-Martin Charcot documented many isolated cases of juvenile Parkinsonism, associated with diplopia, oculogyria, tachypnoea, retropulsion, and obsessional disorders, which were almost certainly post-encephalitic in origin. In 1890 in Italy, following the influenza epidemic of 1889–1890, a severe epidemic of somnolent illnesses (nicknamed the "Nona") appeared. For the few survivors of the Nona, Parkinsonism and other sequelae developed in almost all cases. Between 1915 and 1926, a world-wide encephalitis lethargica pandemic occurred, impacting nearly 5 million people and killing an estimated 1.6 million people. Pandemic of 1915–1926
In the winter of 1916–1917, a "new" illness suddenly appeared in Vienna and other cities, and rapidly spread world-wide over the next three years. Earlier reports appeared throughout Europe as early as the winter of 1915–1916, but communication about the disease was slow and chaotic, given the varied manifestation of symptoms and difficulties disseminating information in wartime. Until Constantin von Economo identified a unique pattern of damage among the brains of deceased patients and introduced the unifying name encephalitis lethargica, reports of the protean disease came in under a range of names: botulism, toxic ophthalmoplegia, epidemic stupor, epidemic lethargic encephalitis, acute polioencephalitis, Heine-Medin disease, bulbar paralysis, hystero-epilepsy, acute dementia, and sometimes just "an obscure disease with cerebral symptoms."