Not all individuals will mount a protective immune response subsequent to vaccine administration. There are many factors that can negatively influence an individual's ability to respond to vaccine. Such factors should be taken into consideration when putting a vaccine protocol to use in a specific individual. The following are considered the most important:

• 1. Host Factors
  • A. Maternal antibody interference
  • B. Immunodeficiencies
    • 1. Congenital
    • 2. Acquired
      • - Infectious agents
      • - Drugs: cytotoxic, glucocorticoids
  • C. Pregnancy
  • D. Age: very young or old
  • E. Pyrexia, hypothermia
  • F. Concurrent or incubating disease
  • G. Stress
    • 1. Anesthesia/Surgery
    • 2. Excessive Transportation
    • 3. Boarding
    • 4. Thermal
  • H. Inadequate nutrition
• 2. Vaccine Factors
  • A. Improper or inadequate adjuvant
  • B. Non-immunogenic strain due to over attenuation
  • C. Inadequate antigenic mass or lack of replication
  • D. Wrong strain of pathogen in vaccine
• 3. Human Error
  • A. Wrong vaccine selected
  • B. Improper storage
  • C. Improper mixing of products
  • D. Inactivated during mixing or use
  • E. Wrong route of administration
  • F. Partial dose of vaccine administered
  • G. Disinfection of skin and equipment inactivates live agent
  • H. Too frequent administration (<21 day interval)* or too long between multiple doses of non-infectious vaccine (>60 days)
  • I. Concurrent use of antimicrobials/immunosuppressive drugs
  • J. Simultaneous use of antisera

* may be true for both same and different antigens