The flow of the cowpox virus depended on vehicles capable of navigating overlapping networks. This pathway introduces the networks and vehicles that mattered most to the transmission and perpetuation of the vaccine in the historic context of mid-nineteenth-century Japan.
The networks through which the virus had to travel were part of the socio-political geography of Tokugawa Japan with its "overlapping geographies of status" (Howell 2005, p. 37). On the one hand, there was the geography of warrior rule, which divided the Japanese lands into fiefs (also called domains). The warrior rulers holding those territories were organized into a hierarchy with the shogun on top. Because of the hierarchical character of these relationships, one can speak of a network only in a very abstract sense. But the domain rulers in Echizen province often did interact with each other as if in a network of equals when coordinating the government of their interlocking territories.
On the other hand, there were the status groups: occupational and residential groups of ordinary subjects that enjoyed a high degree of autonomy. These, too, staked out territories, which were not always congruent with those of warrior rule. Physicians, for example, formed both formal status groups on the level of domains and countrywide or regional networks. These networks of physicians channeled not only the flow of the vaccine, but also the flow of vaccination-related knowledge.
The vehicles carrying the vaccine were of two kinds: either containers made from various materials, or the bodies of children. From the perspective of the virus, children were nothing but temporary hosts—both spaces and vehicles that could move across space. Socially, however, children were imbedded in permanent networks—families and through these in status groups. In addition, arm-to-arm transmission of the virus briefly connected children to each other in an ephemeral kind of network.
Another type of vehicle were written records, which conveyed information about vaccinations across time and space.