This situation can readily be observed in deficiencies of STAT2, TYK2, IFNAR1, and IFNAR2, in which severe viral disease affects some but not all individuals, with a greater penetrance observed for infections with live-attenuated viral vaccines than for common viral infections of childhood (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52). Here, STAT2 is linked to viral infectious disease.