I have 5 pullets right now- 3 are 8 months old and 2 are about 6 months old. I want to get more 4 more chicks from Dodge Grains. However the worker there said they usually don't carry chicks vaccinated against Marek's and 4 is too small of a number to order vaccinated. Is it worth it to get the vaccination? Should I just wait until MyPetChicken sells 4? (Right now they sell a minimum of 15) If one chicken catches the disease, will the whole flock get it? And how likely is it that my chickens will get the disease?