Abstract: Objective  To study the immune efficacy and the influencing factors of BCG. Methods Multi-center, no control, open, prospective cohort study was used to select the study population. The effect and influencing factors of BCG were studied for the baby (<3 months) or the children (<1 years old) PPD negative in 4 districts (city) in Beijing, Jiangsu and Chongqing. The qualified study population was 27 517.  Results  (1) The median of BCG scar was 4.50 mm, the quartile of BCG scar was 3.50-5.00 mm. The BCG scar <1 mm was 223(0.81%, 223/27 517) and ≥1 mm 27 294(99.19%, 27 294/27 517). (2)The median of PPD was 8.50 mm, the quartile was 6.50-11.00 mm. The positive reaction was 26 838(97.53%, 26 838/27 517) and the negative reaction 679(2.47%, 679/27 517). (3) The negative rate of PPD was lower in urban（2.28%，571/25 004）than rural hospitals（4.30%，108/2513）(χ²=38.487, P<0.001). The negative rate of PPD was higher in tertiary hospital（4.18%，199/4760）than others (χ²=119.464，P<0.001). The negative rate of PPD was lower in Beijing（0.53%，57/10 679） than others area （χ²=288.511, P<0.001）. (4) There was 19 cases adverse reaction in the study, the rate of adverse reaction of BCG was 6.90/10 000. The rate of adverse reaction of BCG was different in the three provinces (χ²=32.005, P<0.001). Conclusion  The effect of BCG may be related with urban-rural difference, hospital level, area, et al. The monitoring of BCG vaccine effect should be strengthened. The effect of BCG vaccine should be improved in order to control the tuberculous meningitis and TB.

Key words: Tuberculosis/prevention &, control, BCG vaccine, Vaccination, Injections, intradermal