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Efficacy of Haemophilus influenzae type b capsular polysaccharide vaccine
S B Black1, H R Shinefield, R A Hiatt
1Department of Pediatrics, Permanente Medical Group, Inc., Oakland, CA.
Insights
The Haemophilus influenzae type b (Hib) vaccine showed significant efficacy, preventing most Hib disease cases in children. Early vaccine failures were noted but likely due to chance or pre-immunity development.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- Haemophilus influenzae type b (Hib) disease posed a significant threat to young children.
- Development of an effective Hib vaccine was a public health priority.
Purpose of the Study:
- To evaluate the real-world efficacy of the Haemophilus influenzae type b (Hib) polyribose phosphate vaccine.
- To assess vaccine effectiveness in a large pediatric population over a defined period.
Main Methods:
- A cohort of 120,000 children aged 23-71 months was monitored over two years.
- Case ascertainment for Hib disease involved multiple surveillance methods, including laboratory and hospital record reviews.
- Vaccine efficacy was calculated using retrospective surveillance and matched case-control analyses.
Main Results:
- An estimated vaccine efficacy of 68-69% was observed.
- Four cases of Hib disease were identified as potential vaccine failures, with early occurrences possibly due to chance.
- Adjustments for factors like daycare attendance and parental occupation slightly impacted efficacy estimates.
Conclusions:
- The Hib vaccine demonstrated substantial protective efficacy against Hib disease in the evaluated pediatric population.
- Further investigation into early post-vaccination cases is warranted to understand potential contributing factors.
Abstract:
The efficacy of the Haemophilus influenzae type b (Hib) polyribose phosphate vaccine was evaluated in a population of 120,000 children from 23 through 71 months of age in the Kaiser Permanente Medical Care Program (KPMCP) in Northern California over the 2-year period from June 1, 1985, through May 31, 1987. Approximately 37% of the population were vaccinated by the end of the first year and 60% were vaccinated by the end of the second year. There were 35 cases of Hib disease, 4 of whom were vaccine failures. Cases of Hib disease were identified by multiple modality case ascertainment, consisting of: (1) active surveillance in KPMCP microbiology laboratories; (2) active surveillance on KPMCP pediatric wards by a study physician; (3) retrospective review of computer-stored hospital discharge diagnoses; and (4) a review of all hospitalizations outside the health plan. The medical records of cases, matched controls and a random sample of the population were reviewed to obtain information on vaccination and related variables. Efficacy was evaluated using two complementary methods. In a retrospective surveillance approach, efficacy was estimated to be 68% (95% confidence limits of 4, 89%). In a matched case-control analysis, efficacy was estimated to be 69% (95% confidence limits of -13, 91%). Adjustment for day care attendance and parental occupation slightly reduced the efficacy estimate. Other possible confounders including race, parental education and number of siblings were considered. Four cases of Hib disease were observed within 1 week following receipt of vaccine and before the time when immunity could have developed. There are several plausible explanations for the occurrence of these early cases including the possibility of chance alone.(ABSTRACT TRUNCATED AT 250 WORDS)