This is a short overview about the BCG vaccine and its possible ability to protect from coronavirus infection. It includes a fascinating graph that compares the COVID-19 rates in different countries around the world with different rates of BCG vaccination showing a possible trend in which populations with higher rates of BCG vaccination have had lower rates of COVID-19. There is still a lot of research and work to be done, but it is now the basis of several clinical trials.
https://www.faustmanlab.org/wp-content/uploads/2020/04/BCG2-pagerC-19.pdf