Effectiveness of Haemophilus influenzae type b conjugate vaccine on prevention of pneumonia and meningitis in Bangladeshi children: A case-control study

BACKGROUND: Few Asian countries have introduced Haemophilus influenzae type b (Hib) conjugate vaccine because of its cost and uncertainty regarding disease burden. METHODS: To estimate the effectiveness of Hib conjugate vaccine in preventing pneumonia and meningitis in children age <2 years, an incident case-control study was conducted in a birth cohort of about 68,000 infants in Dhaka city, Bangladesh. DPT vaccine was systematically replaced by a combined Hib-DPT vaccine in selected immunization centers of the study area. Four matched community- and 2 hospital-controls were randomly selected for each confirmed case of pneumonia and meningitis from the study area. RESULTS: About 35% of the infants received each of the 3 doses of Hib-DPT vaccine. There were 2679 children who had a chest roentgenogram. For 475 children, a radiologist and a pediatrician independently identified substantial alveolar consolidation. Following at least 2 doses of Hib vaccine, the preventable fractions [95% confidence intervals (CI)] using community and hospital controls were 17% (-10% to 38%) and 35% (13% to 52%) respectively. Of these 475 cases, 2 radiologists with the World Health Organization concurred with the findings for 343 patients, yielding preventable fractions of 34% (6% to 53%) and 44% (20% to 61%). Fifteen confirmed Hib meningitis cases were identified; the preventable fractions (95% CI) using community and hospital controls, respectively, were 89% (28% to 100%) and 93% (53% to 100%). CONCLUSIONS: The study documented that significant fractions of pneumonia and meningitis in Bangladeshi children age <2 years can be prevented by the Hib conjugate vaccine.