Summary: The finding that severe measles occurs in immunized as well as nonimmunized human immunodeficiency virus (HIV)-infected individuals suggests that both immunologic memory and the initial response to measles may be impaired by HIV infection. That the initial response is affected was supported by the finding that post-measles immunization titers of HIV-infected babies were significantly lower (p = 0.01) than those of normal babies. Poor immunologic memory was evidenced in HIV-infected children by lower titers than in normal children (p < 0.001) and by a continuing decline in measles antibody that was not arrested by reimmunization. Impaired memory appeared to be associated with defective avidity maturation. HIV-infected babies and infants or children had a significantly lower avidity index (AI) than agematched normal children (p < 0.01). HIV-infected adults, who were infected with HIV following infection with measles, did not have AI values significantly different from normal adults (p = 0.18) but had significantly greater values than did HIV-infected babies and children (p < 0.01). Thus, in contrast to infants and children who were infected with HIV before measles immunization, the adult immune response to measles was less affected.
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