Effectiveness of Haemophilus influenzae b conjugate vaccine on childhood pneumonia:: a case-control study in Brazil

Background The conjugate Haemophilus influenzae type b (Hib) vaccine has been highly efficacious in reducing type b H. influenzae meningitis. However, information is limited about its impact on childhood pneumonia after vaccine introduction into the routine programme. This study evaluated the effectiveness of Hib conjugate vaccine in the reduction of community-acquired pneumonia among infants in Central Brazil. Methods A matched case-control study was built into an ongoing prospective population-based surveillance of pneumonia, enrolling 1293 participants between May 2000 and August 2001. Cases (n = 431) were children less than or equal to2 years old hospitalized with radiologically definite pneumonia according to the World Health Organization standard criteria for the interpretation of radiographs for the diagnosis of pneumonia. Two controls (n = 862) without previous hospitalization for pneumonia were identified among children from the same neighbourhood and matched to cases by age stratum (+/-4 months). The Hib vaccination effectiveness was estimated as 1 minus odds ratio (OR). Results The greatest risk factor for pneumonia among children <2 years of age was day-care centre attendance (P < 0.001). Of the study participants, 83.3% (1072/1287) were classified as vaccinated according to immunization card and 16.7% (215/1287) were considered unvaccinated. By using conditional logistic regression the vaccine effectiveness was estimated as 31.0% (95% CI: -9.0%, 57.0%) after adjusting for sex, previous flu-like illnesses, day-care attendance, smokers at home, house ownership, mother's education, and age as continuous variable. Conclusion Under programme conditions the effectiveness of Hib conjugate vaccine in infants with radiologically confirmed pneumonia was 31% (95% CI: -9%, 57%) showing the potential benefit of Hib immunization in the prevention of likely non-bacteraemic pneumonia.