Page 828 - Veterinary Immunology, 10th Edition

“Normal” Toxicity
VetBooks.ir Vaccines commonly elicit transient inflammatory reactions, and

some degree of inflammation is required for the efficient induction

of protective immune responses. This may cause pain. Thus the
sting produced by some vaccines may present problems not only to
the animal being vaccinated but also, if the animal reacts violently,
to the vaccinator. More commonly, swellings may develop at the

reaction site. These may be firm or edematous and may be warm to
the touch. They appear about 1 day after vaccination and can last
for about a week. Unless an injection-site abscess develops, these
swellings leave little trace. Vaccines containing killed Gram-

negative organisms may be intrinsically toxic owing to the presence
of endotoxins that can cause cytokine release, leading to shock,
fever, and leukopenia. Although such a reaction is usually only a
temporary inconvenience to male animals, it may be sufficient to

provoke abortion in pregnant females. Thus it may be prudent to
avoid vaccinating pregnant animals unless the risks of not giving
the vaccine are considered to be too great. Vaccination with either
immune-stimulating complex (ISCOM) vaccines or live

recombinant vectored vaccines against influenza and tetanus may
induce an acute-phase response in horses.

Inappropriate Responses

Vaccines may cause rare but serious allergic reactions. For example,

allergic responses may occur when an animal produces
immunoglobulin E (IgE) in response not only to the immunizing
antigen but also to other antigens found in vaccines, such as egg

antigens or antigens from tissue culture cells. All forms of
hypersensitivity are more commonly associated with multiple
injections of antigens and therefore tend to be associated with the
use of killed vaccines. It is important to emphasize that a type I
hypersensitivity reaction is an immediate response to an antigen

and occurs within a few minutes or hours after exposure to an
antigen. Reactions occurring more than 2 or 3 hours after
administration of a vaccine are likely not type I hypersensitivity

reactions.
Type III hypersensitivity reactions are also potential hazards.

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