Principles of Vaccination

The future of vaccination involves development of protocols that individualize vaccine schedules instead of having every animal vaccinated for every disease. Much discussion is ongoing in the veterinary community regarding vaccination of dogs and cats every 3 years rather than yearly. However, some state and county regulations may still mandate the yearly rabies vaccine regimen, and other states may legislate every 3 years. It is hoped that additional research will yield optimal revaccination intervals. Some studies have suggested that with some vaccines, protective immunity may last for years and annual revaccination may not be necessary. With new information and technology, the twenty-first century will see many changes in vaccines.

Common Vaccine Types That Produce Passive Immunity

Other Types of Vaccines

Administration of Vaccines

The intramuscular and subcutaneous routes are by far the most common methods for vaccine administration. These routes are easily accessible and provide systemic immunity, which is important in many diseases. Some diseases also respond well to local immunity. Vaccines against feline rhinotracheitis and calicivirus, canine infectious tracheobronchitis, and infectious bovine rhinotracheitis may be administered intranasally, or, in some cases, intraocular administration may be used to provide local immunity. After administration of these vaccines, the animal may experience a slight bout of watery eyes and occasional sneezing for a few days.

All of the previously mentioned routes of vaccine administration necessitate that each animal be handled individually. When a large number of animals require vaccination, these routes may not be feasible. Some vaccines may be mixed with drinking water or feed. Others can be aerosolized and inhaled by the animal. For example, on mink ranches, vaccine for canine distemper and mink enteritis may be administered in this manner, or poultry houses may vaccinate for Newcastle disease by aerosolization. The margin for incomplete vaccination is greater when aerosolization or mixing with feed or water is used. Some animals may not drink or eat enough to acquire adequate protection, or the aerosolized vaccine may not distribute equally throughout the room. Vaccine failure may be implicated if these animals contract the disease, whereas in reality, the animal did not receive enough vaccine to gain adequate immunity.

When conventional measures are used for vaccination, it is very important to carefully read the insert provided with the vaccine. Some vaccines may be administered intramuscularly or subcutaneously, but others may be administered by only one route. For example, some rabies vaccines require admin­istration by an intramuscular route to be most effective. Subcutaneous injections should be given according to the manufacturer’s instructions. Care should be used when one is vaccinating a cat to prevent vaccine-induced tumors.

Biologic Care and Vaccine Failure

Biologics (especially modified live and live vaccines) are sensitive to inactivation by heat or sunlight. Clients purchasing vaccines should be provided with a cold pack if needed and should be warned against leaving such biologics in vehicles or in sunlight, where they may become warm and inactivated. Even the performance of killed products can be altered if proper handling and storage measures are not practiced. When these vaccines are shipped from the manufacturer, cold packs are put in the box to provide some refrigeration during shipment. In some areas, it may be advisable to anticipate how much vaccine may be needed during the hot summer months and to stock up on that amount during early spring to prevent shipments from overheating during summer transportation. Once a shipment is received, it should be quickly unpacked and placed under refrigeration. Vaccines should never be frozen because cells may rupture when the vaccine thaws, releasing toxins that can damage tissue or cause tissue death.

Inappropriate care of vaccines may lead to inactivation of the vaccine and may be perceived as a vaccine failure. Actual vaccine failure is relatively uncommon. If vaccines are purchased from a reputable manufacturer, one can be fairly sure that the vaccine provided will be effective. Failure usually occurs because of improper handling, storage, or administration.

Live vaccines are especially affected by concurrent antibiotic therapy. Live and modified live vaccines can be inactivated by chemicals used to clean or sterilize syringes and by the use of excessive alcohol or other disinfectants to swab the skin before injection. As was mentioned earlier, the route of administration may affect the ability of an animal to achieve an adequate immune response. Immunosuppressed, parasitized, stressed, or malnourished animals and those incubating disease are not able to mount an adequate immune response to prevent disease. Clients should always be advised that such problems can occur. In most cases, an adequate immune response is not achieved before 10 to 14 days. An 8-week-old puppy may not develop a strong immune response to protect against an infectious disease if challenged by maternal antibodies because it is not feasible to check immune titers to determine the presence of maternal antibodies. Therefore, it is recommended that puppies receive boosters every few weeks until they are about 4 to 5 months of age. Boosters allow vaccines to produce an optimum immune response. Clients often find it difficult to understand why they need to bring their pet in for boosters. If the reasons are explained and if clients are advised about why they should isolate their pet from animals with questionable vaccination histories, many cases of infectious disease would be prevented among young animals. Clients often perceive one vaccine to be enough or do not understand that their animal is not protected immediately after an injection has been received. Technicians should include this information when educating clients on animal and pet care.

Adverse Vaccination Responses

The most notable risks involving vaccination include residual virulence and toxicity, allergic reactions resulting from hypersensitivity, disease in immunosuppressed animals, possible effects on a fetus, and abortion. The veterinarian assesses these risks before a vaccine is administered. In most cases, the benefits of vaccination far outweigh the risks, but it may occasionally be necessary to omit or delay vaccination because of some of the factors just mentioned.

Vaccinations for Preventive Health Programs