Mycobacterium bovis BCG, a live attenuated tuberculosis vaccine offers protection against disseminated TB in children. BCG exhibits heterologous protective effects against unrelated infections and reduces infant mortality due to non-mycobacterial infections. Recent reports have suggested that BCG vaccination might have protective effects against COVID-19, however it is highly unlikely that BCG vaccine in its current form can offer complete protection against SARS-CoV-2 infection due to the lack of specific immunity. Nonetheless, recombinant BCG strains expressing antigens of SARS-CoV-2 may offer protection against COVID-19 due to the activation of innate as well as specific adaptive immune response. Further proven safety records of BCG in humans, its adjuvant activity and low cost manufacturing makes it a frontrunner in the vaccine development to stop this pandemic. In this review we discuss about the heterologous effects of BCG, induction of trained immunity and its implication in development of a potential vaccine against COVID-19 pandemic.

牛分枝杆菌BCG 是一种减毒活结核病疫苗，可保护儿童免受播散性结核病的侵害。BCG 对不相关的感染表现出异源保护作用，并降低非分枝杆菌感染引起的婴儿死亡率。最近的报告表明，BCG 疫苗接种可能对 COVID-19 具有保护作用，但由于缺乏特异性免疫力，目前形式的 BCG 疫苗极不可能提供针对 SARS-CoV-2 感染的完全保护。尽管如此，由于先天性和特异性适应性免疫反应的激活，表达 SARS-CoV-2 抗原的重组 BCG 菌株可能提供针对 COVID-19 的保护。BCG 在人体中的进一步证明的安全记录、其佐剂活性和低成本制造使其成为阻止这种大流行的疫苗开发的领跑者。