Vaccines to treat encephalitis lethargica: Human experiments at the Neurological Institute of New York, 1929-1940

Background: Encephalitis lethargica, first observed in 1915, became a pandemic. Because of its presumed infectious basis, there were early attempts to treat it with vaccines. The history of the use of these vaccines has not been analyzed. Objective: To document the use of vaccines to treat patients with encephalitis lethargica, and, more specifically, the 1000 patients whose treatments took place with the support of the William J. Matheson Commission at the Neurological Institute of New York, NY (1929-1940). Materials and Methods: Archival materials were analyzed, including the files of the Matheson Commission and the medical records of patients evaluated at the Neurological Institute of New York. Results: Two primary vaccines were used to combat encephalitis lethargica. The Rosenow vaccine was based on clinical and experimental evidence suggesting that the causative agent was Streptococcus viridans. The Levaditi C (later Gay F) vaccine was based on evidence that herpes simplex virus was the cause. During a therapeutic study conducted from 1929 through 1940, 1000 patients received treatment. Assessing therapeutic efficacy was problematic, but the Gay vaccine was considered more effective. Conclusions: Because of its presumed infectious basis, several vaccines were used to treat encephalitis lethargica, with the study at the Neurological Institute constituting the largest organized therapeutic attempt. Many of today's standard clinical trial methods were not practiced, which made it difficult to determine efficacy.