SARS-CoV-2 has been confirmed in over 450 million confirmed cases since 2019. Although several vaccines have been certified by the WHO and people are being vaccinated on a global scale, it has been reported that multiple SARS-CoV-2 variants can escape neutralization by antibodies, resulting in vaccine breakthrough infections. Bacillus Calmette-Guérin (BCG) is known to induce heterologous protection based on trained immune responses. Here, we investigated whether BCG-induced trained immunity protected against SARS-CoV-2 in the K18-hACE2 mouse model. Our data demonstrate that i.v. BCG (BCG-i.v.) vaccination induces robust trained innate immune responses and provides protection against WT SARS-CoV-2, as well as the B.1.617.1 and B.1.617.2 variants. Further studies suggest that myeloid cell differentiation and activation of the glycolysis pathway are associated with BCG-induced training immunity in K18-hACE2 mice. Overall, our study provides the experimental evidence that establishes a causal relationship between BCG-i.v. vaccination and protection against SARS-CoV-2 challenge.


Bao-Zhong Zhang, Huiping Shuai, Hua-Rui Gong, Jing-Chu Hu, Bingpeng Yan, Terrence Tsz-Tai Yuen, Ye-Fan Hu, Chaemin Yoon, Xiao-Lei Wang, Yuxin Hou, Xuansheng Lin, Xiner Huang, Renhao Li, Yee Man Au-Yeung, Wenjun Li, Bingjie Hu, Yue Chai, Ming Yue, Jian-Piao Cai, Guang Sheng Ling, Ivan Fan-Ngai Hung, Kwok-Yung Yuen, Jasper Fuk-Woo Chan, Jian-Dong Huang, Hin Chu


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