Puppies are born with some immunity from their mothers to common viruses (Distemper, Parvo, Hepatitis, Parainfluenza, and Rabies) that can be deadly. Unfortunately, this borrowed immunity which helps the puppy fight off the viruses, only lasts a few months of their lives. To protect the pups, it is important to administer vaccines so they create their own immunity, preferably before the immunity they acquire from their mothers, through nursing, wears off. Some vaccines require repeated dosing. For puppies, the vaccines are often repeated every three weeks, starting as early as six weeks old and concluding at 16 (or older) weeks of age. The rabies vaccine is the exception and is given only once, often at 16 weeks of age. All vaccines are periodically boosted throughout their lifetime to keep their immunity strong.