John Simon has been portrayed as an architect of the implementation of state medicine, who fundamentally changed the character and extent of public health policy in Britain. However, as his biographer, Royston Lambert, has shown, Simon experienced considerable difficulties when trying to put his sanitary policies into practice. The same problems arose with vaccination. On paper, the regulations issued by the Medical Office of the Privy Council in the early 1860s fundamentally changed the relationship between central and local government over the running of public vaccination. They gave the Medical Office a role alongside the Poor Law Board in supervising public vaccination. At the local level, the regulations aimed to reorganize provision, changing a system of public vaccination that allowed a degree of autonomy into a highly uniform, national scheme. The regulations also changed the relationship between public vaccinators and the state. Where vaccinators had once just been the employees of boards of guardians, now their qualifications and standards of work were also set by, and scrutinized by, central government.

However, in shaping this policy, Simon had not won the approval of the agencies responsible for implementing public vaccination: the Poor Law Board, boards of guardians, and public vaccinators. This was to prove to be his undoing. The Medical Office of the Privy Council had no power to enforce regulations, and Simon failed to convince the various agencies of the need for reform.