The 1837 Great Plains smallpox epidemic spanned 1836 through 1840, but reached its height after the spring of 1837 when an American Fur Company steamboat, the S.S. St. Peter, carried infected people and supplies into the Missouri Valley. More than 17,000 Indigenous people died along the Missouri River alone, with some bands becoming nearly extinct. Having witnessed the effects of the epidemic on the Mandan tribe, fur trader Francis Chardon wrote, "the small-pox had never been known in the civilized world, as it had been among the poor Mandans and other Indians. Only twenty-seven Mandans were left to tell the tale." The Commissioner of Indian Affairs in 1839 reported on the casualties: "No attempt has been made to count the victims, nor is it possible to reckon them in any of these tribes with accuracy; it is believed that if [the number 17,200 for the upper Missouri River Indians] was doubled, the aggregate would not be too large for those who have fallen east of the Rocky Mountains." History Smallpox has afflicted Native Americans since it was carried to the western hemisphere by the Spanish conquerors, with credible accounts of epidemics dating back to at least 1515. Smallpox was particularly deadly in the plains because no one in these communities had been exposed, and developed immunity before. This is why mortality rates were so high. By the 1730s smallpox had made its way west in Canada and northern United States. The Assiniboine First Nation had controlled much of this territory, but were forced to give it up as their population decreased dramatically. Along the Missouri River the Arikara population was reduced by half by the end of the 1730s. Other communities that were decimated in the 1730s by smallpox include the Lower Loup, Pawnee of Nebraska, Cherokee, and Kansa. In short, smallpox in the 1730s devastated Indigenous communities living on the North American plains. It was found in 1796 that infecting a person with the mild cowpox infection would provide immunity to smallpox. As its use became widespread in Europe its deployment in North America was also praised by Thomas Jefferson as a means for preserving lives. Unfortunately, supply lines for the vaccine were faulty and it was not until the 1830s that a large portion of the Indigenous population was vaccinated, and even here it was limited to beyond the Southwest. Early vaccination efforts by the Hudson's Bay Company