The early series of vaccinations insures a good level of protective immunity in a young puppy or kitten. This is the age when they are most susceptible to many contagious diseases. A series of vaccines are given because it is unknown exactly when your puppy’s or kitten’s antibodies, received from it’s mom, are dissipating. At this time their own immune system must be stimulated with the vaccines to protect themselves. This loss of mom’s antibodies generally occurs somewhere between 6 and 12 weeks of age. Adult pets will usually need yearly vaccine boosters, but will not need to repeat the series.