Fundamentals of Pharmacology for Veterinary Technicians

Chapter 21

Vaccines

Immunity

• Nonspecific immunity– Includes things such as physical barriers,

mucus production, inflammation, fever, and phagocytosis

– Directed against all pathogens; is the initial defense against invading agents

• Specific immunity– Takes over when the nonspecific mechanisms

fail– Targeted for a specific antigen; has memory– Arises from B- and T-lymphocytes

Types of Immunity

• Cell-mediated immunity– T-lymphocytes directly attack the invading

antigen– Important for protecting against intracellular

bacterial or viral infections, fungal diseases, and protozoal diseases

• Antibody-mediated immunity– B-lymphocytes produce antibodies that react

to antigen– Important for extracellular phases of systemic

viral and bacterial infections and protection against endotoxin and exotoxin-induced disease

Ways to Acquire Specific Immunity

• Active immunity– Arises when an animal receives an antigen that

activates B- and T-lymphocytes– Creates memory

• Passive immunity– Arises when an animal receives antibodies from

another animal– Provides immediate onset of immunity, but the animal is

protected for a shorter time (no memory)

• Natural immunity– Acquired during normal biological experiences

• Artificial immunity– Acquired through medical procedures

Vaccines

• A vaccine is a suspension of weakened, live, or killed microorganisms administered to prevent, improve, or treat an infectious disease

• Types of vaccines:– Inactivated (killed): made from microbes, microbe parts,

or microbe by-products that have been chemically treated or heated to kill the microbe

• Contain adjuvants (substances that enhance the immune response by increasing the stability of the vaccine in the body); may cause vaccine reactions

• Advantages: safe; stable; unlikely to cause disease• Disadvantages: need repeated doses; possible reactions

Vaccines

• Types of vaccines (cont.):– Attenuated (modified-live): microorganisms go

through a process of losing their virulence (called attenuation), but must be able to replicate within the patient to provide immunity

• Advantages: immunity lasts longer; has better efficacy and quicker stimulation of cell-mediated immunity than killed vaccines

• Disadvantages: possible abortion; can produce mild forms of the disease; can shed into the environment; proper handling/storage is critical

Vaccines

• Types of vaccines (cont.):– Live: made from live microorganisms that may

be fully virulent• Advantages: fewer doses needed; last longer;

inexpensive; adjuvants not needed• Disadvantages: residual virulence that requires

carefully handling– Recombinant: a gene or part of a

microorganism is removed from one organism (usually the pathogen) and inserted into another microorganism

• Advantages: fewer side effects; effective immunity; varied routes of administration

• Disadvantage: increased cost

Vaccines

• Types of vaccines (cont.):– Toxoids: “vaccine” used against a toxin that

has been deactivated by heat or chemicals, but is still able to stimulate antibody production

• Advantage: provides protection against toxin• Disadvantages: shorter duration of effectiveness;

may contain adjuvants

– Antitoxins: substances that contain antibodies obtained from an animal that has been hypersensitized to neutralize toxins

• Advantage: quick protection against a toxin• Disadvantages: short-lived protection; may contain

preservatives that can cause reactions

Vaccines

• Types of vaccines (cont.):– Antiserum: antibody-rich serum obtained from

a hypersensitized or actually infected animal• Advantage: provides quick protection against a

microorganism• Disadvantages: shorter duration of effectiveness;

may contain adjuvants

– Autogenous: vaccine produced for a specific disease in a specific area from a sick animal

• Advantage: provides protection against the specific organism in a specific area

• Disadvantage: may contain endotoxin and other by-products found in the culture

Vaccines

• Types of vaccines (cont.):– Multiple-antigen vaccines are called polyvalent– Polyvalent vaccines contain more than one antigen

• Contain a mixture of different antigens and are more convenient to administer because fewer injections are needed

• Adverse reaction increases as the number of antigens increases

– To be approved, must show that each part of the polyvalent vaccine induces the same level of immunity as does the single-antigen vaccine

– Monovalent vaccines are vaccines with only a single antigen present

• Using several monovalent vaccines may expose the animal to higher levels of adjuvants

• Must give more injections

Maternally Derived Antibodies

• Maternally derived antibodies are antibodies that offspring receive passively from their mothers, either from colostrum or via the placenta

• Maternally derived antibodies give the offspring disease resistance for a few days and provide variable antibody levels for up to nine weeks

• To enhance this protection, young animals receive vaccinations and booster vaccinations to ensure appropriate immunity– Booster vaccines are needed because effective

vaccination varies among individuals, because of variable levels of maternal antibodies

– Booster vaccines also allow antibody levels to rise to satisfactory levels

Vaccine Reactions

• Although vaccines are considered safe, vaccine reactions can occur

• All vaccine reactions must be recorded in the medical record

• Typical vaccine reactions: – Location reactions at the injection site– Fever– Lethargy– Vomiting– Salivation– Difficulty breathing– Vaccine-associated sarcomas in cats– Autoimmune hemolytic anemia in dogs

Issues in Vaccine Use

• Consider the following with all vaccine protocols:– Vaccine issues

• Proper care and handling• Proper route of administration• Proper use (do not mix vaccine products)• Proper dose

– Patient issues• Animal age• Freedom from disease• Concurrent use of medication• Pregnancy• Environment

Vaccine Protocols

• Practice of annual vaccination is now under debate

• One way to discover when revaccination is necessary is via the antibody titer– An antibody titer is a serum test that reveals the level of

antibody to a particular antigen in a particular individual– Antibody titers are expressed as 1:2, 1:4, etc., a ratio

that represents the dilution at which the immune response is still adequate

• Core vaccines are recommended for all individual animals

• Noncore vaccines are recommended only for individual animals deemed to be at high risk for contact with the organism

Species-Specific Vaccine Protocols

• Examples of vaccines available for a variety of species are listed in the textbook