Vaccination against smallpox was a time-sensitive, sequential procedure. The goal was to immunize the human body against smallpox by implanting the cowpox virus (Variolae vaccinae), which belonged to the same family as the smallpox virus but resulted in a much milder case of illness. In the late eighteenth century, several physicians across Europe had proven the protective qualities of the cowpox virus, and British doctor Edward Jenner pioneered a method that involved extracting lymph from a liquid-filled pock on the arm of a cowpox patient and transfer it to the arm of an uninfected person. Because the cowpox virus was not contagious among humans, physicians needed to intervene. The vaccinator typically made several incisions with a lancet on the upper arm of the receiving child to imbed the vaccine into the skin. The number of incisions depended on the age of the child. Before the procedure, physicians had to confirm that the child was not currently suffering from any other illness such as scabies that might interact with the vaccine and interfere with immunization. 

Next, vaccinators had to monitor the child's reaction. After three or four days, they checked whether pocks had appeared at the incision site. Between six and eight days after transfer, the pocks were considered ripe for extraction, and vaccinators could decide to use the child as a supplier for vaccinating other children. In Japan, physicians used the term tōbo ("pox base;" literally: "pox mother") for children who provided lymph for further vaccinations.

Part of the vaccinator's job was to detect so-called "false pocks" (or "spurious pocks"). In some cases, vaccinated children developed pocks that superficially resembled genuine cowpox but in fact constituted reactions to other infections or bacterial contamination. Proper classification of "false pocks" was crucial because the children who developed them remained unprotected from the smallpox virus. If a child was found to display false pocks, vaccinators usually decided to revaccinate and repeat all the necessary steps.