In the late 19th and early 20th centuries, the relatively mild variola minor type was common in Minnesota and killed few people.
The worst period had been 1871–1872, when 273 people died, but since then the average had fallen to fewer than 15 deaths a year.
In the fall, when people began to huddle indoors, the disease spread: 27 died in October, 66 in November, and 149 in December.
Had the disease affected both cities' populations equally, there would have been 91 deaths in Saint Paul and 129 in Minneapolis.
It had more flophouses, shelters, and boarding houses, all of which pressed sometimes sickly people into close quarters.
Minneapolis public health officers, perhaps overwhelmed by the scope of their problem, acted less efficiently in training hospital workers, tracing sources of the virus, and warning schools, businesses, and families of danger when infection appeared.
Saint Paul officials isolated as many of the ill as they could in a "pest house" far from the center of town.
Although smallpox vaccination is almost 100% effective, public health officers had no power to make people protect themselves.