The most serious condition involving the immune system in young puppies is an inadequate immune system (immunodeficiency). The immune system is inherently responsible for warding off infections, which may be life threatening. Demodectic or red mange
is an infection with a mite that virtually only occurs in puppies who are immunodeficient. A puppy with a poor immune system is not only susceptible to many diseases, but it may have a poor response to important puppy vaccinations. By not responding to vaccinations, we mean that the puppy's immune system will not recognize the fact that it has been vaccinated and will not produce antibodies needed to fight the diseases it was vaccinated against.
A puppy may be immunodeficient for many reasons. The biggest cause is simply genetics. The puppy was born with a poor or inadequate immune system. Other puppies in the litter may be just fine, however. Some puppies may develop diseases such as distemper, which may hinder or suppress the immune system. Puppies, which fail to nurse, will not have adequate antibody intake from the mother's first 'immune rich' milk called colostrum. The unnursed puppy is thus immunodeficient.
It is a fact of medicine that a portion of puppies will be immunodeficient for any of the above reasons. For this reason, even with modern advancements in vaccinations, some puppies will be inadequately protected against infectious diseases. This is not a fault of the vaccines, but rather a genetic or developed problem with the puppy's own immune system. It is not practical to test every puppy to identify the state of the immune system. We just have to recognize that immunodeficiency problems may arise even in the seemingly healthy and vaccinated puppy.