BCG vaccination and active tuberculosis prevention: a three-year study

ABSTRACT

Six to eight million people are infected with tuberculosis [TB] annually throughout the world, out of which 2 to 3 million die. BCG vaccination and its efficacy are always used in tuberculosis control planning. There are different rates of BCG vaccination efficacy in the world from 0 to 80%. BCG vaccine has different efficacy in endemic and non-endemic areas. The prevalence of tuberculosis in Iran is high; therefore it was necessary to perform a study in this regard. This was a case-control descriptive study conducted from 2001- 2003. There were 50 cases of active pulmonary tuberculosis [according to WHO definitions], and 100 controls without tuberculosis admitted for other reasons. Vaccination was done in 10 [20%] people in the case group and 36 [36%] people in the control group [OR 43%].Thus vaccine efficacy was calculated to be 57% in this study from the equation VE=1-OR [CI 95% between 0.04-0.81]. Twenty percent of vaccinated people have been protected from active tuberculosis in this study. In this study vaccine efficacy was 57% [CI 95% between 4-81%], and protection rate of vaccinated people against active tuberculosis was 20%. The effectiveness of BCG vaccine is not constant in all situations and old age and past history of contact with TB patients are confounding factors causing the low efficacy of the vaccine. While case control studies have limitations; thus, similar studies should be planned in different parts of our country for more accurate results: