It’s sometimes difficult to know what vaccines can and cannot do.

Welcome to the world of vaccinology, a science-based study of vaccines and the claims their manufacturers make for protection and production enhancement. Using it allows your veterinarian to select the best products for a particular challenge. 

Here is a brief primer:  

The immune system
No vaccine is 100 percent effective in 100 percent of the animals. Too many variables from stress, pre-existing diseases, nutrition and management, stage of life or production exist to ever get 100-percent efficacy. Our goal in vaccination is to enhance the animal’s immunity to minimize clinical problems and prevent spread throughout the herd.

The immune system has two parts -— the humeral and cell-mediated systems. Humeral immunity stimulates cells to produce antibodies. The studies and charts that deal with vaccine titers convey that information. The higher the titer, the more antibodies present to fight against a particular disease. Most vaccines stimulate the humeral system. Some require a first vaccination to prime the system, with a second dose given within a few weeks to restimulate and booster the immunity, thereby raising the titer level. Additional vaccinations, usually given every few months or yearly, or natural exposure to the disease will again booster the titers -— and hopefully keep the antibody level high enough to protect the animal.

The cell-mediated side of the immune system only recently became easily quantifiable. This system involves the defense cells of the body, such as white blood cells, and the enzymes and chemicals they produce to engulf and destroy foreign organisms in the body. Cell-mediated immunity is the primary system involved with the rejection of transplant organs and grafts and for our intradermal skin tests, such as with tuberculosis. It is also important in the defense against bacterial diseases and some viruses.

The vaccine’s role is to stimulate one or both of these systems. Vaccinology helps us know which system needs to be primed for a specific disease, and which vaccines will affect that system.

Cattle are protected from diseases such as rabies, BVD, IBR, and some forms of leptospirosis through cell-mediated immunity. Not all vaccines will properly stimulate this branch of the immune system. Modified-live viral vaccines generally induce a much better cell-mediated response than killed vaccines. They also produce antibody or humeral protection as well. Once stimulated, some killed vaccines can be used as booster shots. They will stimulate both branches of the immune system, and are generally safer to give at all stages of life. Newer vaccines for bacterial diseases can better stimulate both branches and are generally safe for all animals.

To know if a product will protect our livestock, we must look at the research and challenge studies. These are generally done in real-world situations where both vaccinated and non-vaccinated animals are challenged with the disease. Data for both clinical signs of the disease and the immune system response are given for both groups so that you can judge the difference the vaccine makes. Without these studies, the charts on titers and response mean very little to our real-world application of the products.

Make careful selections
All vaccines are not equal. What works in one region may not be effective in another. Our role as veterinarians is to wade through the data and use our vaccinology skills to determine which products to recommend. Producers should rely on our independent judgment when selecting products and protocols to help protect their herds.

Jim Brett is a practicing veterinarian in Montezuma, Ga.