Milkmaids

The discovery of the role cowpox can play in preventing smallpox infection was a total accident. (Not the one you think) Smallpox inoculation was becoming widespread in England, and doctors checked for a "successful" inoculation by looking for smallpox pustules. If an inoculation was deemed unsuccessful the patient had to be reinoculated until a reaction was observed. One day after an unsuccessful inoculation, a farmer, grasping at straws, mentioned that he had recently had cowpox. This triggered the doctor's curiosity resulting in research into the instances of patients, (particularly farm workers) who had had cowpox before having no reaction to the smallpox inoculation. Many doctors collected a lot of data, and had many discussions before hypothesising that recent cowpox infection could prevent smallpox infection. While Edward Jenner did test the hypothesis, the story about him noticing the unblemished milkmaids and having a Eureka! moment, is an entirely fictional account designed to make immunisations more appealing to the general public.

Although much less likely to be fatal, cowpox is not without symptoms and the pustules are far more painful and debilitating that those cause by smallpox. Cowpox lesions "mature" into large, painful blisters, most often on the hands (transferred through skin contact, from the cow's udder to the milkmaid's hands), preventing the sufferer from performing everyday task or working. It also only lasts up to 3 months. Had Celeste contracted cowpox from being a milkmaid, the pox would have begun on her hands, making it impossible to hide the infection with her clothes. She would not have been able to bare the agony of a corset over the boils she inexplicably had all around her torso. She would certainly not have been able to work as a prostitute, fully clothed or not, due to the pain of the lesions. And she would have been free of infection before her son was born, many years before the events in the episode.