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Effectiveness of Haemophilus influenzae type B conjugate vaccine on prevention of pneumonia and meningitis in Bangladeshi children: a case-control study.
by Baqui AH, El Arifeen S, Saha SK, Persson L, Zaman K, Gessner BD, Moulton LH, Black RE, Santosham MThe Pediatric infectious disease journal.
Article Abstract:
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.
Socio-economic Disparities Probably Invalidate Bangladesh Hib Study Conclusions
By: Jacob Puliyel - Mon 12/17/2007 PMWe read the article by Baqui et al1 with great interest. The case control study concludes that there was more pneumonia among those not vaccinated with Hib-DPT. We are not surprised by this. This was essentially a case-control study on top of a vaccine trial. The intervention (vaccination) was neither randomized nor was blinding performed.
The authors state that the socioeconomic status of those receiving HibDPT and those receiving DPT was similar. Yet, when they selected controls for the children admitted with pneumonia, they choose children from a higher socioeconomic background. Intuitively, poverty and malnutrition are related to infections like pneumonia and diarrhea. Ideally, the controls must have been matched for socioeconomic status and nutritional status to rule out the effect of these factors on the effectiveness of the vaccine . Alternatively, the samples could have been stratified according to socioeconomic status and nutritional status and vaccine efficacy could have been looked for, separately in the different stratified groups. If differences were found, it would prove that there is a role of confounding and/or effect modification due to malnutrition and socio-economic status. If so, pooling across different strata of socio-economic strata is not appropriate as it might lead to bias (Simpson's paradox).
Instead, the authors look for potential differences in 'propensity to immunize' and performed statistical adjustments for some socio-demographic variables. It is understood that statistical adjustment may not remove all confounding, especially if there is a strong confounding role of any factor. The fact that malnutrition plays in disease etiology has not been reckoned at all. These limitations suggest that the conclusions of the authors must be treated with considerable caution.
Proper randomized trials are needed before the efficacy of Hib vaccination is established, especially in regions where extensive surveillance done by international originations have demonstrated low incidence of the disease2,3. Before we rewrite the Koch's postulates based on this study, we must be certain we are on firm grounds. The enthusiasm of the sponsors of the study should not supplant scientific objectivity.
Sujith Dhanasiri MPhil Centre for Economics of Mental Health, Institute of Psychiatry Kings College, London.
Jacob M. Puliyel MD MRCP MPhil
Department of Pediatrics
St Stephens Hospital
Tis Hazari
Delhi 110054 India
Email: puliyel@gmail.com
References
1. Baqui AH, ElArifeen S, Saha SK, Persson L, Zaman K, Gessner BD, Moulton LH, Black RE, Santosham M. Effectiveness of Haemophilus influenzae Type B Conjugate Vaccine on Prevention of Pneumonia and Meningitis in Bangladeshi Children: A Case-Control Study. Pediatr Infect Dis J. 2007;26:565-571.
2. Invasive Bacterial Infections Surveillance (IBIS) Group of the international Clinical Epidemiology Network. Are Hemophilus influenza infections a significant problem in India? A prospective study and review. Clin. Infect. Dis. 2002; 34:949-57.