ENO2 and COVID-19: The primary objectives of 15 trials (94%) was to evaluate BCG-mediated NSE on mortality, infections of any origin, and respiratory infections [4,5,6,7,8,16,32,33,35,36,37,38,39,40,41]; five trials (31%) specifically investigated BCG-mediated NSE on COVID-19 [16,35,36,37,40]; one (6%) trial was conducted to study prevention of Mycobacterium tuberculosis infection with BCG revaccination [34].