Page 822 - Veterinary Immunology, 10th Edition

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FIG. 25.3 The actual antibody responses in a herd of cattle
vaccinated against bovine viral diarrhea type 1. Antibody log titers
of less than 3 are not considered significant. Log titers greater than
9 may reflect a secondary response as a result of prior infection or
previous vaccination. Note that these results represent a normal
distribution and reflect the responses to most vaccines. Vaccination
success is not guaranteed. (Data courtesy Dr. T. Hairgrove).

Another type of vaccine failure occurs when the normal immune
response is suppressed. For example, heavily parasitized or
malnourished animals may be immunosuppressed and should not
be vaccinated. Some virus infections induce profound

immunosuppression. Animals with a major illness or high fever
should not normally be vaccinated unless for a compelling reason.
Stress may reduce a normal immune response, probably because of

increased steroid production; examples of such stress include
fatigue, malnutrition, and extremes of cold and heat. Studies have
shown that surgical neutering at or near the time of first vaccination
does not impair the antibody responses of kittens. This type of
immunosuppression is discussed in detail in Chapter 40. The most

important cause of vaccine failure of this type is passively derived
maternal immunity in young animals, as described in Chapter 23.
Analysis of an outbreak of influenza in racehorses has shown

some interesting and important factors that appeared to determine
vaccine effectiveness. Thus when the effect of age was analyzed, it

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