Efficacy of BCG vaccination of the newborn: evaluation by a follow-up study of contacts in Bangui.

BACKGROUND

The efficacy of Bacillus of Calmette and Guérin (BCG) vaccination given at birth is still controversial. We therefore conducted a study in Bangui (Central African Republic) to estimate the protection afforded over the first seven years of life by BCG administered at birth.

METHODS

One thousand children who had lived in contact with a recently diagnosed case of contagious tuberculosis were followed up for a period of 6 months in order to detect the occurrence of tuberculosis. Diagnosis of tuberculosis was made through a scoring system. Vaccine efficacy (VE) was calculated on the basis of the relative risk of contracting tuberculosis according to vaccination status.

RESULTS

The efficacy of BCG was estimated to be 71% (95% confidence interval: 56-81%). This result remained practically the same after changing the definition used for tuberculosis cases (VE = 75% for a threshold with a score of 15 instead of 6, VE = 74% when only confirmed cases were considered). There was no difference between the two groups in the variables measuring intensity of contact with the source of contamination, but there was a difference in age distribution. Vaccine efficacy adjusted for this factor was the same as the crude VE.

CONCLUSION

This study, based on a methodology that controls for most of the risks of bias inherent to field efficacy measurement, confirms the protective capacity of neonatal BCG against childhood tuberculosis. Therefore BCG vaccination at birth must remain a public health priority especially in countries with high incidence of the disease.