MT-ND2 and COVID-19: The fmtDNA was isolated from heated serum samples of both healthy individuals and COVID-19 patients, and their quantities were determined using RT-qPCR specific primers (Table S2), targeting three genes and one non-coding sequence: cytochrome c oxidase subunit III (COX-III), NADH dehydrogenase 2 (ND-2), and the DNA displacement loop (D-Loop-I and D-Loop-II) (Fig. 1A).