A foster parent also provides time to build active immunity in those animals that are susceptible such as kittens, puppies, even some adults. (heartofthevalleyshelter.org)
From there, booster shots continue to stimulate active immunity. (spotmagazine.net)
All kittens require 2 - 3 sets of booster vaccines in order to develop active immunity against the common infectious diseases. (vcahospitals.com)