IFNG and infection: However, TST reversion was evident in 22% of guinea pigs exposed for up to 5 months to TB patients and this correlated with clearance of an established infection.13 Tuberculin skin test (TST) and QuantiFERON (QFT; a commercially available interferon (IFN)‐gamma release assay IGRA test) reversion are also evident in humans.14, 15 In a recent study BCG revaccination of adolescents had 45.4% efficacy against sustained Mtb infection.