Hi there, Welcome to BYC.. what part of California are you in?
Did you already hatch these chicks? If so how old are they?
Are you in the New Castle quarantine/euthanasia zone?
Possible vaccines I know about are
Coccidiosis (irrelevant to me if your husbandry is good and you aren't overcrowding, it's very preventable).
Marek's (only effective if given shortly after hatch. Not welcome at my place because it just masks symptoms and doesn't actually stop the disease).
New Castle's (I'm very unfamiliar with the virus or the vaccine) But being in California, would definitely suggest you research it more.
Fowl Pox (maybe more key in areas with tons of mosquitoes like Florida. Most birds will overcome it naturally IF they do get it).
Have healthy chicks by giving proper feed, space, and fresh (poo free) water. Don't diminish these things with low quality treats like scratch or cracked corn which provide energy but NOT the vitamins, minerals and amino acids that are added into our formulated rations.
Keep things simple by feeding your whole flock a non-medicated starter or Flock Raiser, with oyster shell on the side for active layers... Instead of trying to keep the chicks out of layer feed. I never switch and the extra protein (about 4% more) has decreased the harshness and time spent molting for my flock since feathers are made from 90% protein and it's amino acids.
Hope this is helpful!