A distemper shot is a vaccine that protects dogs against the canine distemper virus, which is a highly contagious and often fatal disease that attacks the respiratory, gastrointestinal, and nervous systems of dogs. The distemper shot is usually given in combination with other vaccines, such as the rabies vaccine and DAPP (Distemper, Adenovirus Type 2, Parvovirus, and Parainfluenza) . The distemper vaccine is critical for puppies or immune-compromised adult dogs, as they are at the highest risk of contracting the disease. The vaccine is not 100% effective against disease prevention, but it greatly reduces the risk of contracting distemper when administered properly. The vaccine is usually given to puppies at six weeks old and then every three to four weeks until 16 weeks old, and immunity may last for three years or more. It is important to follow your veterinarians recommendations and complete the proper dose of the distemper vaccine to ensure maximum protection.