IgG avidity refers to the net force by which multivalent antigens are bound to by multivalent antibodies. A primary exposure to an antigen is associated with appearance of IgG antibodies with low avidity, but over time there is “affinity maturation” with the appearance of IgG antibodies that show a high avidity.
An IgG avidity enzyme immunoassay involves use of the denaturation agent diethylamine (DEA) to determine avidity.
Primary measles vaccine failure:
(1) indicates that the person never formed protective antibodies after the vaccination
(2) is associated with an IgM immune response on exposure to Measles virus
(3) is associated with a low IgG avidity (<= 30% according to Mercader et al, < 30% according to Pannuti et al)
Secondary measles vaccine failure:
(1) protective antibodies did form to vaccination but have declined over time
(2) tend to be associated with mild clinical measles on re-exposure
(3) is not associated with an IgM immune response
(4) is associated with a high IgG avidity (> 70% according to Mercader et al)
where:
• An intermediate IgG avidity (31-69%) was considered equivocal according to Mercader et al.
