Evaluation of the efficacy of routine BCG vaccination: a case-control study.

A case-control study was conducted in a metropolitan region of Cairo, Egypt to determine the protective efficacy of routine BCG Vaccination of infants against childhood pulmonary tuberculosis. A total of 175 cases of children suffering from pulmonary tuberculosis were obtained over 8 months period from hospitals likely to admit such cases in Cairo. Each case was matched to two controls for the district of residence. Vaccination status of cases and controls was ascertained by asking the mothers and confirmed by examination of the left arm of the study children for the scar of BCG vaccination. The overall crude efficacy of BCG vaccination was found to be 53% (CL: 68%, 31%), dropping to 49% (CL: 57%, 25%) after controlling for the confounding effect of crowding index. Potential biases in the study design and their role in over or underestimation of the vaccine efficacy were discussed.