Research progress on specific and non-specific immune effects of BCG and the possibility of BCG protection against COVID-19

Abstract

Bacille Calmette-Guérin (BCG) is the only approved vaccine for tuberculosis (TB) prevention worldwide. BCG has an excellent protective effect on miliary tuberculosis and tuberculous meningitis in children or infants. Interestingly, a growing number of studies have shown that BCG vaccination can induce nonspecific and specific immunity to fight against other respiratory disease pathogens, including SARS-CoV-2. The continuous emergence of variants of SARS-CoV-2 makes the protective efficiency of COVID-19-specific vaccines an unprecedented challenge. Therefore, it has been hypothesized that BCG-induced trained immunity might protect against COVID-19 infection. This study comprehensively described BCG-induced nonspecific and specific immunity and the mechanism of trained immunity. In addition, this study also reviewed the research on BCG revaccination to prevent TB, the impact of BCG on other non-tuberculous diseases, and the clinical trials of BCG to prevent COVID-19 infection. These data will provide new evidence to confirm the hypotheses mentioned above.

Routing Innate and Adaptive Immune response against M. tuberculosis and boosting Mycobacterium bovis Bacillus Calmette Güerin (BCG) vaccine immunity through prime boost protocols

“…2) The induction of a nonspecific response, now called trained immunity [155,157,158,162] . This type of response might be beneficial to support early clearance of infection to the same pathogen, to other nonrelated respiratory pathogens [163] , or even against other chronic diseases (cancer) [164] . Indeed a specific response follows a nonspecific innate immune response (trained immunity) to generate a memory innate-like response independent of T and B cells [162,165,166] .…”

Exploring BCG vaccination as a novel approach to prevent recurrent herpes labialis

“…Research suggests that BCG vaccination induces three types of non-specific immune responses: trained immunity, heterologous immunity, and anti-inflammatory effects. 2 , 3 These immune responses have been used to prevent and treat a range of diseases, including HSV-1, human papillomavirus, and COVID-19 3 , 4 , 5 , 6 ( Fig. 1 ).…”