Specific antibody deficiency (SAD) is associated with an impaired antibody response after administration of polysaccharide vaccines.
Diagnostic features:
(1) presence of normal levels of IgG, IgM and IgA
(2) impaired IgG antibody formation to polysaccharide vaccines such as:
(2a) Hemophilus influenzae type B
(2b) Streptococcus pneumoniae
(3) frequent and recurrent bacterial infections, primarily involving the respiratory tract
This condition underlies the need to serotype isolates of Hemophilus influenzae and Streptococcus pneumoniae causing invasive disease in vaccinated individuals.
Differential diagnosis:
(1) Children < 2 years of age may not respond well to polysaccharide vaccines.
(2) A more significant immunodeficiency may be indicated by either a poor response to protein-based vaccines or by the presence of other abnormal laboratory findings.
(3) Problems with a polysaccharide vaccine or its administration.
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