Antibody of polyribophate of Haemophilus influenzae type b in infants and children: effect of immunization with polyribophosphate.

Antibody to polyribophosphate, the capsular polysaccharide of Haemophilus influenzae type b, was measured in healthy ambulatory children by a radioactive antigen-binding assay. Titers fell from birth through nine months of age, then increased until six years, when they plateaued. Antibody activity was not correlated with the child's sex, ethnic status, or area of residence. Doses of 0.2-50 microgram of polyribophosphate given as single or booster doses had similar effects on antibody activity. Of 368 doses given to infants two to six months of age, 7% produced a significant antibody response; of 95 doses given to infants seven to 12 months old, 17% produced a response. The geometric mean titers of antibody resulting from immunization with polyribophosphate given at various times in relation to diphtheria-pertussistetanus vaccine did not differ significantly from one another or from titers observed in infants given only the latter vaccine. These data indicate that purified polyribophosphate will not provoke humoral immunity in young infants against H. influenzae type b and that it should no longer be considered as a candidate vaccine for this purpose.