Hi Agapanthus
Poultry flocks can be vaccinated against salmonella, Newcstle disease, Infectious bronchitis and Mareks disease, amongst others.
The breeder should know what the parent flock has been vaccinated against. Most hybrid flocks are vaccinated against the first three. Breeders of Silkies will often have also vaccinated against Mareks.
If the young have not been vaccinated it does not mean that they will die, in fact some breeders recommend not vaccinating to promote natural immunity. Your local vet should know if there are any diseases prevalent in your area.
Loz ;)