Since its origin in the Wuhan province of China in December 2019, Coronavirus Disease 19 (COVID-19) has spread to most parts of the world and has infected millions of people. However, the significant variability in the mortality rate across the world indicates some underlying factors, especially the immunity factors that may have a potential role in this variability. One such factor that is being discussed and tested is the Bacillus Calmette-Guerin (BCG) vaccine. The available evidence suggests that BCG vaccination provides broad protection against respiratory infections as well as other infections. Therefore, BCG may prove to be a barrier for COVID-19 infection and may offer a ray of hope. In this review, we contrasted BCG vaccination program with COVID-19 mortality and analyzed trained immunity and cross protection against unrelated pathogens due to BCG vaccination. On analyzing the available data, we observed that countries without universal BCG vaccination policy are severely affected, while countries having universal BCG policies are less affected. Based on these data, we propose that the SARS-CoV-2 related qualified immunity, cross protection against unrelated pathogens and COVID-19 impact variations could be partly explained by the different national policies regarding BCG childhood vaccination. The combination of reduced morbidity and mortality may make BCG vaccination a potential new tool in the fight against COVID-19.
Keywords: BCG vaccine; COVID-19; SARS-CoV; corona virus; mortality rate.; trained immunity.
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