Response to Haemophilus influenzae type b conjugate vaccine in chronically ill premature infants.

Twenty-two premature infants with chronic lung disease (median gestational age 28 weeks) received polyribosylribitol phosphate-outer membrane protein conjugate Haemophilus vaccine at 2 and 4 months of chronologic age. The proportions with antibodies to polyribosylribitol phosphate at levels > 1 microgram/ml after doses 1 and 2 were 27% and 55%; geometric mean titers were 0.43 and 0.73 microgram/ml, significantly lower than values for term infants.