(…)Using fluorometry, total DNA in all vials tested exceeded the regulatory limit for residual DNA set by the US Food & Drug Administration (FDA) and the World Health Authorization (WHO) by 36–153-fold for Pfizer and 112–627-fold for Moderna after accounting for nonspecific binding to modRNA. When tested by qPCR, all Moderna vials were within the regulatory limit, but 2/6 Pfizer lots (3 vials) exceeded the regulatory limit for the SV40 promoter-enhancer-ori by 2-fold. The presence of the SV40 promoter-enhancer element in Pfizer vials raises significant safety concerns. This study emphasizes the importance of methodological considerations when quantifying residual plasmid DNA in modRNA products, considering increased LNP transfection efficiency, and cumulative dosing presents significant and unquantified risks to human health.