Mother Nature knows how to take care of puppies. When they come into this world and begin to nurse, their mothers' milk contains immunity-producing proteins. These maternal antibodies provide the same protection for the puppy that the mother has. If her immunity level was high, these antibodies may last up to three months. If they were low, the puppy may only have five or six weeks of protection before immunity begins to diminish.

If a puppy receives a vaccine before the antibodies are gone, the vaccine does not take effect and provides no additional immunity. The puppy is protected by whatever immunity the mother has delivered. The vaccine is meant to fill the gap in case maternal antibodies are not sufficient or wane early. Of all the types of disease protection, parvovirus immunity from the mother lasts the longest. In some puppies this can last up to four months.

Some veterinarians recommend that owners keep puppies away from other dogs and places where other dogs usually congregate until about four months of age. This is when the puppy's own immune system takes charge. Many holistic veterinarians recognize that early socializing is important to the behavioral development of puppies and say it's okay to take puppies out to socialize before four months of age. Discuss the pros and cons with your veterinarian before deciding.