Postlicensure surveillance for Haemophilus influenzae type b invasive disease after use of Haemophilus influenzae type b oligosaccharide CRM197 conjugate vaccine in a large defined United States population: a four-year eight-month follow-up.

Haemophilus influenzae type b (Hib) oligosaccharide CRM197 (HbOC-HibTITER, Lederle-Praxis) conjugate vaccine was approved for use in infants in October, 1990, as a result of an evaluation of 61,080 infants in whom the vaccine was found to be safe and effective. This report details a 4-year 8-month period of surveillance after the licensure of this vaccine in the large defined United States population from which these children were drawn. The population analyzed consisted of approximately 240,000 children from 0 through 8 years of age in a total health plan population of 2,500.000. During this period 16 cases of invasive Hib disease were identified. Nine had not received any type of Hib vaccine, 2 had received the unconjugated polysaccharide Hib vaccine and 4 had received the HbOC vaccine. Of this latter group one toddler had received a single dose of the vaccine at 18 months of age < 24 hours before becoming ill, two 7-month-old infants had received a single dose of the vaccine at 2 or 3 months of age and one 3-year 4-month-old child had received three doses of HbOC vaccine as an infant but had never received the recommended booster dose. The 16th case occurred on July 10, 1994, in a 7- year-old child who at 18 months of age had received a single dose of PRP-D (ProHIBIT; Connaught) conjugate Hib vaccine. The use of HbOC conjugate Hib vaccine in this population has coincided with the virtual disappearance of invasive Hib disease in children 0 through 8 years of age with no cases of invasive Hib disease occurring in the past 3 years and 4 months after the use of this vaccine. During this period no concomitant increase of H. influenzae disease with other types of H. influenzae organisms has been seen in the study population.