During the Spanish flu pandemic of 1918 the best medical minds in the country were focused on the problem of discovering the cause of the flu and how to prevent it — and they failed. Sherman’s Vaccine was developed in response to the pandemic. Essentially it was a “stew” of numerous bacterial strains (“influenza-bacillus-pneumococcus-streptococcus-staphylococcus-micrococcus-catarrhalis vaccine”), including that of the “influenza bacillus,” which had been identified in the 1890’s as the probable cause of influenza. The bacillus resisted attempts to completely prove or disprove its essential role in the disease and so remained for a long time our “best guess.” The human influenza virus was not isolated until 1933; this sample of Sherman’s Vaccine dates to 1937.