IFNG and infection: When assessing the utility of measuring SARS‐CoV‐2‐specific T‐cell responses to identify those with confirmed prior infection, Youden's index revealed an optimal cut‐off value of >22·70 pg/ml IFN‐γ, achieving a sensitivity of 96·0% (95% CI 80·5–99·8%) and specificity of 84·4% (95% CI 74·7–90·9%) (AUC = 0·94 (95% CI 0·90–0·99); p < 0·0001; Figure 1F).