Persistence of antibody responses to Haemophilus influenzae type b polysaccharide conjugate vaccine in children with vertically acquired human immunodeficiency virus infection

Background. Recurrent bacterial sepsis is common in pediatric HN infection and immunization against Haemophilus influenzae type b (Hib) is recommended. Long term persistence of anti-Hib antibody and the need for, or timing of, a booster dose has not been adequately studied. Methods. Immunogenicity during a 12-month period following immunization with Hib-tetanus conjugate vaccine (ACT-HIB(R); Merieux) was evaluated in 48 vertically HIV-infected children and 36 uninfected children, born to HIV-positive mothers. A titer of anti-Dib polysaccharide antibody of greater than or equal to 0.15 mu g/ml was considered to indicate short term and greater than or equal to 1 mu g/ml long term protection. Results. At 1 month postvaccination 36 (100%) uninfected and 42 (88%) HIV-infected children achieved titers of greater than or equal to 1 mu g/ml. However, by 1 year titers had dropped below this value in 18 (43%) infected compared with only 4 (11%) uninfected children (chi square, 9.7; P = 0.002). Although the rate of fall of antibody titer was greater in uninfected than in infected children, this was no longer the case after adjustment for the 1-month postimmunization titer. The rate of antibody titer decline was not significantly related to HIV disease status or to either the age-related CD4 count at the time of immunization or the change in age-adjusted CD4 count during the 12 months after immunization. Conclusions. Not only was the initial antibody response to Hib conjugate vaccine decreased in children with HIV infection and AIDS but also 1 year later only 57% of the initial responders had persisting titers above the level associated with long term protection. The need for reimmunization of children with HIV infection against Hib requires further evaluation.