It depends on how old the pups are when they got their first shots, and whether or not they still have their maternal antibodies, which if they do, will destroy the vaccine when it is injected. Hence the need for repeating the vaccines.
Each pup ingests a different amount of colostrum (first milk after birth), which contains the Mom's antibodies. Eventually these antibodies go away, and this is when the pup can be successfully vaccinated. As the timing is different for each pup, 3-4 vaccines are given to establish immunity.
I believe it is now recommended to begin the first vaccines at 10 weeks of age, and booster in 4 weeks at 14 weeks old and again at 18 weeks. I believe if vaccines are not started until 16 weeks of age, then only two sets of vaccines are necessary to establish immunity. |