Abstract
Emerging evidence suggests that T-cells play a significant role in COVID-19 immunity both in the context of natural infection and vaccination. Easy to use IGRA assays including QFN SARS are considered attractive alternatives to more "traditional" but laborious methods for detection of SARS-CoV-2-specific T-cell responses. In our Letter we are proposing explanations to an apparently lower than expected T-cell responses (44 % reactive individuals) reported by Krüttgen et al in a small cohort of healthy double vaccinated individuals. These results could have been affected by reporting raw optical density values instead of calculated Interferon-ɣ concentrations which is supported by unexpectedly low mitogen responses in healthy individuals. This study highlights an importance of adhering to good laboratory practice principles as well as overall importance of accurate T-cell immunity assessment using IGRA assays.