Question: Why are the puppy vaccine series important?

Answer: Puppy and kitten vaccines are very important because the "series of vaccines" prevent them from contracting many serious diseases.  Mother Nature protects the neonatal (first born to several weeks old) puppies and kittens through the antibodies provided in the colostrum (first milk) when the puppies/ kittens are just born in the first day.  That is why it is so important that they nurse right away after birth.  The colostrum is only protective to the new borns if they nurse right away at least the first few hours of life. If they do not get their colostrum, they are not protected at all and are at great risk. These antibodies are absorbed into the newborn's blood stream from their upper GI tract.  Generally, they protect the newborns until they are 6 weeks of age or so but this varies some depending on each infectious agent that make up the vaccine. These protective antibodies are referred to as maternal antibodies. 

Puppies and kittens must be vaccinated in a series of vaccines.  Most veterinarians begin vaccinations at 6-9 weeks of age after the puppies/kittens are weaned.  Vaccinating before 6 weeks of age is not recommended because the immune system is not mature enough yet and may be harmful. Boosters are needed at 3-4 week intervals (I prefer 3 weeks) until they reach 15-18 weeks of age (9-12 wks, 12-15 wks, & 15-18 wks). Typically the booster protocol can be stopped when the puppy or kitten reaches 15 weeks of age or older.  If they get a late start, for example a puppy or kitten does not get vaccinated until they are older (ex.12 weeks or older), then they will only need a booster in 2-4 wks. Getting a late start is not a good idea.  If a puppy / kitten does not start until 12 weeks or older, he/she is at greatest risk of infection and totally not protected if exposed in those earlier weeks from 6 weeks until that first dose is given at 12 weeks or older in this example. 

The reason a series is required is that the maternal antibodies especially for canine parvovirus or feline distemper (panleukopenia or feline parvovirus) can interfere or block the puppy’s or kitten’s immune response to the vaccine until the maternal antibodies in their blood streams decrease enough below the “blocking” threshold so that the immune response can properly occur which may not occur until the puppy’s or kitten’s reach 12-16 weeks of age.

Rabies vaccine do not require a series.  It only requires one dose at 12 weeks of age or older, and the next booster is required one year later. If given before 12 weeks of age, it is likely that maternal antibodies will block their immune response, so these early rabies vaccinations are not recognized as protective, so that puppy or kitten will require another vaccination when he/she reaches 12 weeks or older.