Routine puppy vaccinations against Parvovirus and Distemper are essential to ensuring your puppies health. Puppies are protected against these viruses until they are approximately 10-12 weeks old through the antibodies that they received from their mother. After that, they are susceptible to becoming infected with the viruses. That is why it is essential that they receive the full vaccine regimen. Veterinarians recommend that you give the first vaccine at approximately 6-8 weeks of age and then repeat every 3-4 weeks until they reach 16 weeks of age. This is to ensure that they receive the full round of vaccines and have developed their own protection at close to the same time that their mother's antibodies are no longer effective. There is a window of susceptibility during which time the puppies mother's antibodies are no longer effective and they have not developed their own protection. This is approximately between 8-12 weeks of age. It is really important to keep the puppy away from environment's where they could possibly be exposed to the virus during this time.
Parvovirus and Distemper virus are both found throughout the environment and can survive for long periods of time in the soil. It is imperative that you keep young unvaccinated puppies away from any yards where there was a known positive puppy for at least 1 year.
Both of these viruses cause severe intestinal distress. Basically, they cause the intestines to shed their lining. These are the cells that absorb water and nutrients out of the intestines. Therefore, the puppy ends up losing a lot of water (i.e. diarrhea) and losing a lot of weight due to the inability to absorb nutrients. The shedding of the intestinal lining is also very painful. Many puppies, especially small breeds, do not survive this loss of water and nutrients.
If you choose not to vaccinate your puppy and they survive puppyhood, their odds of contracting the viruses does decrease significantly. However, unvaccinated adult dogs can still contract the viruses.