Protection provided by Haemophilus influenzae type b conjugate vaccines in Los Angeles County: A case-control study

C. M. Vadheim, D. P. Greenberg, E. Eriksen, L. Hemenway, P. Christenson, B. Ward, L. Mascola, J. I. Ward

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The objective was to assess the degree of disease control and to evaluate the protective efficacy of licensed Haemophilus influenzae type b (Hib) conjugate vaccines (HbOC, PRP-OMP, PRP-D) used routinely in children 2 to 35 months of age. We conducted a case-control study in Los Angeles County between January 1, 1991, and December 31, 1992, and a cohort analysis of Hib cases between 1983 and 1992. For the case-control study 105 cases of invasive Hib disease were identified and 767 geographically and age-matched controls were selected by random digit telephone dialing. Sixteen HbOC vaccine failures occurred >14 days after a single dose of vaccine, 6 vaccine failures after 2 doses and 3 failures after 3 doses; 2 cases occurred 6 and 12 days, respectively, after an initial dose of HbOC. The protective efficacy of a single HbOC vaccine dose was 71.1% (95% confidence interval (CI), 37.5 to 87.2%). After 2 doses the efficacy was 88.8% (95% CI, 59.5 to 96.9%) and after 3 doses it was 94.4% (95% CI, 68.0% to 99.0%). Similar 95% CIs were seen for 1 and 2 doses of PRP-OMP vaccine. Adjustment of efficacy estimates for potential confounding variables did not significantly alter the results. Despite relatively low rates of immunization (20 to 60%) the rates of Hib disease decreased strikingly between 1990 and 1992 (from 24.2 to 4.4/100 000 children <5 years of age). The HbOC conjugate vaccine, used predominantly but incompletely during this period, provided substantial protection against invasive Hib disease in children immunized between 2 and 35 months of age. Optimal protection was afforded only after 3 doses of HbOC vaccine, but appreciable protection was afforded by 1 or 2 doses. The decreased rates of Hib disease suggest that a reduced likelihood of disease was afforded to unvaccinated children as well.

Original languageEnglish
Pages (from-to)274-280
Number of pages7
JournalPediatric Infectious Disease Journal
Issue number4
StatePublished - 1 Jan 1994
Externally publishedYes


  • Haemophilus influenzae disease
  • Haemophilus influenzae type b
  • vaccine efficacy

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Microbiology (medical)
  • Infectious Diseases


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