After studying smallpox outbreaks, Haygarth decided that it spread only by contagion from person to person and was transmitted primarily by an airborne vapor over a very short distance. He drew up “Rules of Prevention” warning those with smallpox to avoid going out in public and those who were susceptible from entering any house that held a smallpox patient. Everyone and everything touched by any discharges from a patient should be washed and exposed to fresh air and all medical attendants must wash their hands. Then he launched a campaign in Chester for mass inoculations. Inoculating groups of people at the same time could also reduce the odds that they would transmit smallpox.
With his ally Thomas Falconer, Haygarth founded a "Society for Promoting Inoculation at Stated Periods and Preventing the Natural Smallpox" in Chester. They raised donations to pay local doctors to perform the procedure and to pay poor families for bringing their children. All the doctors volunteered to participate without charge, increasing the fund for the families.
One concern was that recently inoculated children might spread smallpox. Even worse, some families exposed their children deliberately. To prevent these problems, the Society offered two payments to any poor family that (1) inoculated its children and (2) faithfully followed Haygarth's “Rules for Prevention”. The Society wrestled with the ethics of paying parents for inoculations but concluded that it could be considered compensation for the wages lost while they nursed their children. They also hired an “inspector” to follow up with the families and ensure that they observed the quarantine rules. Mass inoculations were not new, but this may have been the first time anyone tried to create widespread immunity by offering a reward to families for inoculations.
At first the society was successful, inoculating hundreds of children, suppressing incipient epidemics, and halving the death rate in Chester from smallpox. In 1781, however, with their funds dwindling, they decided to stop paying families for inoculating their children and focus on rewards for obeying the rules of prevention. When the scheme was first initiated, they thought paying for the inoculation itself was necessary to overcome “inveterate prejudices,” against the procedure, but it had come to be seen as a bribe for doing something wrong.