B900
Vaccines

Introduction: Veterinary biologics are products designed to prevent, treat, and even diagnose animal disease. They generally work by stimulating the body’s immune system to produce antibodies for fighting off infection.

1. Active Immunity: Active immunity is obtained when the individual’s own immune system responds to an infectious disease. The active immune response may be stimulated by either the disease itself or a vaccine.
   
   
2. Passive Immunity: This type of immunity against an infectious disease is obtained by receiving antibodies made by another individual’s immune system. The most common example of passive immunity occurs when a lamb/kid consumes colostrum. Colostrum is the first milk produced by the mother. It is rich in antibodies against diseases for which the mother has immunity. When the newborn nurses from its mother for the first time, it receives passive immunity against those diseases. Over time, however, the maternal antibodies wear out, and the newborn must actively mount its own immune response. Because of this decline in maternal antibodies, it is essential to vaccinate at a young age.
   
   
3. Vaccine: A vaccine is a mixture of killed or modified microorganisms or their parts, administered to help prevent sickness from infectious diseases.
   
   
4. Adjuvant: A necessary component of inactivated vaccines, adjuvants are additives to the vaccine suspension that help the body’s immune system recognize the dead virus particles and mount an effective immune response against them. Aluminum salts are usually the adjuvant type seen in commercial veterinary vaccines.
   
   
5. Viral Vaccines:
   1. Modified live virus vaccines (MLV vaccines) - These vaccines are composed of living viruses that have been altered to avoid causing the disease being vaccinated against. Despite being changed, these vaccines will still stimulate an immune response by the body. The changing process (attenuation) of these viruses is usually accomplished through repeated culturing of the virus in a tissue to which it is not adapted. MLV vaccines do not require the use of adjuvants, are less likely to produce vaccination reactions, and stimulate a good immune response with fewer doses than a killed virus vaccine. However, some MLV vaccines have been known to actually cause the disease they are trying to prevent. This occurs when the attenuation or changing process is not complete.
   2. Killed (inactivated) virus vaccines - These vaccines are composed of whole or parts of the killed virus to which the body mounts an immune response. Generally, killed virus vaccines are more stable for storage and less likely to cause the disease being vaccinated against; however, they are more likely to produce vaccination reactions due to the high level of virus particles and the adjuvants that are used.

      Modified Live Vaccines:
      Advantages 

      • One dose required 
      • Faster immune response
      • Stronger and more durable response
      • Fewer post vaccination reactions

      Disadvantages

      • Not recommended for pregnant animals or animals in contact with pregnant animals 
      • Possible viral shedding to other animals
      • Improper handling may inactivate the vaccine

       

      Killed Virus Vaccines:
      Advantages 
      • Recommended for pregnant animals
      • Stable in storage
   
   Disadvantages
   • Multiple doses required
   • Weaker immune response
   • Shorter duration immune response
   • Adjuvants may cause reactions
   • Hypersensitivity reactions more common
     
     
6. Bacterial Vaccines: Bacterins are killed whole bacteria or their parts. Some of the bacterin vaccines are among the most notorious for producing vaccination reactions. Like killed virus vaccines, bacterins are unlikely to cause disease through retained virulence (ability to cause disease) and are more stable for storage.
   
   
7. Toxoids: This is an inactivated toxin (poison), administered to stimulate the body’s immune response against the poison itself, rather than against the organism that produces it. Probably most common is the tetanus toxoid. Due to the delay in producing a response and because of their longer lasting effect, toxoids are used in prevention rather than treatment.
   
   
8. Antitoxin: An antitoxin is purified serum from another individual, containing antibodies against a toxin. Antitoxins do not produce an immune response and are not technically vaccines. They provide immediate protection against a toxin and are given for treatment of existing disease, rather than for long-lasting prevention. Antitoxins that are used in veterinary medicine include tetanus antitoxin and Clostridium perfringens antitoxin. Antitoxins are a form of passive immunity.
   
   
9. Antiserum: This is purified serum from another individual that contains antibodies against different organisms (bacteria or viruses). Antiserum is another form of passive immunity.

Vaccines In General:
A vaccine is designed to help the animal develop a certain level of resistance to a targeted disease. Although a vaccine may be at work to provide an animal with immunity from a disease, there are several factors that affect the level of protection. Even with vaccinations, the immune system can be overwhelmed by other challenges, rendering the vaccine ineffective at preventing the disease.