Why Even Give a Vaccine to Animals? Modified-Live vs. Killed Vaccines – Which Is Better?

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First we need a short review of how a vaccine works in the body.

With any vaccine, the trick is to have a strain of organisms mimic their disease-causing cousins closely enough that the animal’s “active” immune system will be ready to recognize the disease-causing pathogen. Then when infection enters the body, it will either be interrupted before the disease occurs or the severity of the resulting disease will be reduced.

Note that vaccines can’t prevent infection. The offending pathogen must get inside the body to come under fire from the vaccine-stimulated “active” immune system. There is an “innate” immune system in the body also. Like a firewall in an apartment complex, the body has “innate” firewalls to prevent infection. For example, bacteria that cause pneumonia must first overcome the mucous and cilia lining in the upper airways of the lungs. Then they must get past the defense cells in the lower airways and finally penetrate the respiratory tract membranes.

If the bacteria are not able to break through all of this, infection is prevented and vaccine-stimulated immunity will not be necessary. For example, compare the mucosa and cilia “innate” immune system to a firewall in an apartment complex and the sprinkler system to the vaccine-stimulated “active” immune system. Since the apartment complex firewall keeps the fire out of the next section of apartments, the next section’s sprinkler system will not be activated. If the fire breaches the firewall, the sprinklers will be activated to fight the fire. When the innate immune system breaks, the active immune system begins fighting the pathogens.

When we give a vaccine, the body builds antigens to fight that disease. It is like giving a blue print of a sprinkler system to the plumber for installation in building.

So asking, “Why even give a vaccine?” is like asking, “Why even build a sprinkler system?” When we don’t give a vaccine it is like not providing a blueprint for a sprinkler system and not installing sprinklers. For certain diseases, animals have no “innate” immune system (firewall) or pathogens move through the “innate” immune system very fast. To protect our animals. we really need to give a vaccine.

Veterinarians always recommend (and in many cases require) Blackleg vaccine in all cattle, even when animals are kept on the same farm. The reason for this is within 48 hours of observable symptoms of Blackleg almost all animals are dead. Blackleg spores live in the soil in all of North Carolina. Since researchers have not found a way to eradicate it, a producer’s only wise option is to vaccinate.

Another question, “Which is best … Modified-live vaccine (MLV) or killed vaccines?” is a common one.

First let’s review these two terms. A live vaccine contains bacteria or a virus that has been modified (MLV). This means they’ve lost their disease-causing ability (attenuated) or are administered by a route that prevents them from causing clinical disease, although the bacteria or virus is still alive. Killed vaccines are just what the name says – a solution of bacteria or virus which was attenuated (lost their disease-causing ability) but also resulted in bacteria or virus death.

MLV and killed vaccine (two types of blueprints for a sprinkler system in the building analogy) have their individual advantages and disadvantages.

Some positive attributes of MLV vaccines include:

  • A strong, long-lasting immune response that is achieved with fewer doses
  • Virus vaccines’ ability to quickly stimulate antiviral protection
  • A minimum occurrence of allergic reactions.

Some positive attributes of killed vaccines include:

  • Greater stability in storage
  • The unlikelihood of containing traces of contaminating vaccine.

Another important thing the producer must remember, since this is occurring at a microscopic level, vaccinations need to be tested in the field where stress is an everyday occurrence. Ultimate determination of a vaccine’s merits comes from controlled tests conducted under field conditions similar to the production setting.

Evaluating a vaccine’s effectiveness is very difficult because so many management factors can overwhelm a vaccine’s effect. Therefore, specific vaccine recommendations should be made by a veterinarian familiar with the disease problems they typically experience on farms in the surrounding community. Also, to assist in choosing the correct vaccine, veterinarians must be familiar with a farmer’s operation, type of cattle, and management style.

The choice to vaccinate will ultimately depend on the targeted pathogen as well as the nature of the relationship between the animal, pathogen, vaccine, and management style. The bottom line for the builder in the apartment complex example is, “Did the builder provide the plumber the money and blueprint to install a sprinkler system that will prevent a fire from spreading throughout the whole building?” The bottom line for vaccinations to work is, “Did the producer provide his animals a low stress and healthy environment at vaccination time, so their bodies can produce the antibodies necessary to fight off the disease?”

A very good article in Beef Magazine, Modified-Live Vs. Killed Vaccines – Which is Better?, written by Gerald Stokka & Louis Perino, gives a review of the MLV vs. killed vaccine.

N.C. Cooperative Extension brings you researched information, backed by our land grant universities; NC State University and NC A&T State University. If you have any questions call our Lincoln County Center office of N.C. Cooperative Extension at 704-736-8461 and ask for the Livestock Extension Agent, Glenn Detweiler.