ANTIBODY-RESPONSE OF MEXICAN INFANTS TO HAEMOPHILUS-INFLUENZAE TYPE-BCAPSULAR POLYRIBOSYLRIBITOL PHOSPHATE - DIFFERENCES BETWEEN NATURAL AND VACCINE-INDUCED (OLIGOSACCHARIDE-CRM(197) CONJUGATED VACCINE) IMMUNIZATION

In this study we compared natural vs. induced Haemophilus influenzae t ype b (Hib) anti-capsular polyribosylribitol phosphate (PRP) antibody response in a low socioeconomic population. One hundred twenty five 2- month-old children received the complete HbOC vaccine immunization sch eme and a booster dose at 15 months of age, One hundred twenty five no n-immunized children served as the control group. Serum Hib anti-PRP a ntibody titers were determined by ELISA in all children. We found at t he end of the primary immunization scheme an antibody concentration of 27.28 mu g/ml in the immunized group vs. 7.48 mu g/ml in the control group. The antibody response was mainly of the IgG1 class in both grou ps. After the booster dose the antibody concentration was 30.14 g/ml i n the vaccinated group vs. 6.06 mu g/ml in the control group (p <0.01) . Ninety nine percent of immunized and non-immunized infants had titer s greater than 1 mu g/ml. These results confirm that immunization with the HbOC vaccine induces an important increase in anti-PRP specific a ntibody titer, but they also demonstrate that natural exposure induces responses higher than those referred as protective (1 mu g/ml).