Moreover, repertoire diversity metrics, including Chao1 estimators (a measure of species richness), Gini-Simpson indices (probability of interspecific encounter), and inverse Simpson indices, were decreased for COVID-19 samples compared to healthy donor samples, notably for the AB, ISB-S CD4, and ISB-S CD8 datasets (Fig. 1B, C, S1B). This evidence concerns the gene CD4 and COVID-19.