[Is it possible that BCG vaccine protects against COVID-19?]

A number of clinical trials are currently underway worldwide to assess whether BCG, the old vaccine against tuberculosis, can protect against COVID-19 infection. In this Perspective, we briefly outline the background, the immunological mechanisms (in particular induction of 'innate immune memory' or 'trained immunity'), and further considerations for the potential future use of BCG against viral and other infections