I don't know what the situation is over there, but over here, vaccinations aren't necessarily the panacea they are sometimes thought to be, IMHO. (Other than, perhaps, the day-old Marek's vaccine.) A lot of people don't realize that, with some vaccinations, the bird can shed skin cells that can migrate to other birds, thereby infecting them with the disease, even though the bird that shed them is immune. There was a huge outbreak a few years ago because someone vaccinated their bird, which then spread the disease to many others. Those birds then took the disease home to their flocks, and devastated them. Be very careful, and talk to a lot of people before you vaccinate.
Don't dismiss that hen with the black flecks. If she shows good type as an adult, she can be used to produce good cockerels, who need the black.
Sorry, I do not mean to derail, but do you know which vaccines cause chickens to shed actively contagious virus?