Table II.

POTENTIAL REASONS FOR VACCINE FAILURE

•Insufficient time after vaccination to develop immunity •Something happened to the vaccine to make it ineffective •The physiologic status of the animal impaired the response to the vaccine •The animal was immunosuppressed at some point after vaccination •The animal was exposed to an overwhelming challenge dose of infectious agent •The duration of immunity after vaccination was not adequate •Important antigenic differences exist between the vaccine and field strains •Interference when multiple vaccines are administered concurrently