Letter in response to article in journal of infection: Impact of routine infant BCG vaccination on COVID-19. Issue 1 (January 2021) - Levi, Miriam; Miglietta, Alessandro; Romeo, Gianpaolo; Bartolacci, Simone; Ariani, Filippo; Cipriani, Francesco; De Filippo, Carlotta; Cavalieri, Duccio; Balzi, Daniela