Capsular polysaccharide Haemophilus influenzae type b vaccine: clinical and immunologic responses to two vaccines.

The clinical reactions and immunologic responses to two Haemophilus influenzae type b capsular polysaccharide vaccines were studied in 24- to 36-month-old children. A candidate vaccine (Connaught) induced greater than or equal to 1.0 microgram/ml of antipolysaccharide antibody in 37 (61.7%) of 60 infants 24 to 26 months of age; this compared with 8 (38.1%) of 21 infants 24 to 36 months of age given a licensed vaccine (Praxis). Reactions to both vaccines within 24 hours of administration were minimal; a smaller percentage of recipients of the candidate vaccine were asymptomatic (P less than 0.05). The lower levels of antibody production than previously reported may necessitate a reevaluation of current recommendations.