There are several types of vaccines currently available for use in dogs: modified live virus (MLV), inactivated or killed virus, and the newest recombinant technologies—live vectored, subunit, and DNA vaccines. Modified live virus vaccines are vaccines that contain virus that is alive and will replicate when in a dog, but has been modified so that it shouldn’t cause the actual disease. These vaccines tend to generate a quick and full immune response. Killed virus vaccines are vaccines with dead virus, which will not replicate in a dog, so they are incapable of causing disease. Instead, they rely on surface antigens, along with immune stimulants called adjuvants, to stimulate an immune response.
Modified live vaccines are more effective and produce longer-lasting immunity than do killed vaccines. Results for recombinant vaccines indicate that immunity can last as long as MLVs. With all types of vaccines, booster shots are necessary to maintain an adequate level of protection. The frequency of needed boosters shots is very variable, and depends on the disease involved, the individual vaccine, the dog’s own immune system, and whether he has been exposed to the disease agent naturally.
Recombinant vaccines are among the newest products in the rapidly emerging biotechnology market. The technology relies on the ability to splice gene-sized fragments of DNA from one organism (a virus or bacteria) and to deliver these fragments to another organism (the dog), where they stimulate the production of antibodies.
For the live vectored version, genes from a canine antigen may be put into a noninfectious virus. Antibodies are stimulated; there is no replication of the antigen. Subunit vaccines stimulate immunity to a part of the antigen of an infectious organism. These are set up to provide the most immunity for the least amount of antigen used. With DNA vaccines—currently experimental for dogs—only a small amount of DNA from the infectious agent is used.
Thus, recombinant vaccines deliver specific antigen material on a cellular level without the risk of vaccination reactions associated with giving the entire disease-causing organism. This represents a truly new development. It is expected that recombinant vaccines will soon replace MLVs and whole killed vaccines for many, if not most, canine infectious diseases.