SAFETY AND IMMUNOGENICITY OF A NEW HAEMOPHILUS INFLUENZAE TYPE b VACCINE IN INFANTS UNDER ONE YEAR OF AGE

Abstract

64 healthy infants, 2-3 months old, were randomly assigned to one of three vaccination groups which received either diphtheria pertussis-tetanus (DPT) vaccine, Haemophilus influenzaetype b capsular polysaccharide polyribosyl-ribitol phosphate (PRP) vaccine, or PRP + P (with pertussis adjuvant) vaccine in three doses at intervals of 2 months. Local and systemic reactions occurred most frequently after DPT vaccination and least frequently for PRP alone. Data for 60 infants from whom complete sera sets were available indicated that 70% of the infants who received three doses of PRP+P showed 2-fold or greater increases in titres of antibody to PRP with final values above the level assumed to give protection against invasive H. influenzae type b disease (≥0·15 μg/ml). In contrast, less than 10% of the infants who received PRP vaccine alone showed 2-fold or greater increases.