Our subgroups analysis by age at BCG vaccination revealed that both early vaccination (less than one year old) (summary OR 0,64; 95% CI [0.4–1.01])14,22,23,27,28,30,32 and later vaccination (summary OR 0.26; 95% CI 0.04–1.63)25,26 were associated with a lower risk of childhood leukemia, although the latter estimate lacked precision as there were only two studies.