The few published studies on serum zonulin levels and COVID-19 come from cohorts/case series of United States of America (Giron et al., 2021; Josyabhatla et al., 2021; Yonker et al., 2022), Italy (Oliva et al., 2021) and Turkey (Kılıç et al., in press) only. This evidence concerns the gene HP and COVID-19.