This pathway shows how both the smallpox virus and the smallpox vaccine (that is, the variolae vaccinae virus) perpetuated themselves over time and moved across space. It explains the properties of these two viruses, as well as the conditions and interventions they required to move from host to host. The pathway concludes with a discussion of popular Japanese ideas about smallpox and smallpox vaccines at the time of the vaccine's introduction in the middle of the nineteenth century, by inspecting a contemporary woodblock print advertising vaccinations.

One of the most memorable chapters in the history of smallpox vaccination in Japan is the story of the vaccine's importation. In the decades before 1849, Japanese and Dutch physicians arranged for the vaccine to be sent from Batavia in the Dutch East Indies or from China on several occasions, but failed each time because the virus did not survive the long sea journey through tropical climates. In 1849, Japanese physicians finally succeeded at reconstituting the vaccine from scabs brought to Nagasaki on a Dutch ship and immunized a local child. Within Japan, the vaccine could be moved more easily through arm-to-arm transmission. But distribution still hinged on the presence of a network of physicians who were willing to share the vaccine rather than monopolize it as a potentially lucrative source of income.

The tale of the importation and spread of the vaccine in Japan has already received much attention (Jannetta 2007). But there is another, equally important aspect to the story of the vaccine that has only begun to be told: its perpetuation over time. Because of the spatial and temporal limitations imposed by the biological properties of the smallpox vaccine, physicians faced major hurdles in trying to keep it in circulation. As Yanagisawa Fumiko has noted, the vaccination rate in Fukui prefecture (which roughly overlaps with Echizen province) only crossed the eighty-percent mark in the second half of the 1880s (Yanagisawa 2018, 59). This figure suggests that even under the centralized structure of the Meiji state with its emphasis on public health and countrywide record-keeping, the goal of full coverage was not easy to attain.