Currently, Bacille Calmette-Guerin(BCG) is still the only admitted
vaccine to prevent
tuberculosis around the world. The target population is infants and children, but its protective efficacy is limited. As more and more studies have shown that re-vaccination with BCG protects against
tuberculosis in adults, BCG can also induce non-specific immunity against other
respiratory diseases and some
chronic diseases by training immunity, especially the immune effects against
COVID-19. At present, the epidemic of
COVID-19 has not been effectively contained, and it is worth considering whether
BCG vaccine can be used as an intervention to prevent
COVID-19. The WHO and China do not have a policy to support BCG revaccination, and as more and more BCG
vaccines are discovered, whether selective revaccination can be carried out in some high-risk populations and whether the
vaccine can be used more widely have led to intense discussions. This article reviewed the effects of specific immunity and non-specific immunity of BCG on
tuberculosis and non-tuberculous diseases.