Optimized protocol for a quantitative SARS-CoV-2 duplex RT-qPCR assay with internal human sample sufficiency control

•Duplex RT-qPCR assay provides SARS-CoV-2 viral copy number across >7 logs.•Limit of detection 6 copies/10 μL RNA or 150 copies/mL VTM.•Amplification of human RNA controls for all steps from swab taking to PCR.•2.4 % of samples (15/618) are inadequate and require re-sampling.•E copy number normalized to RNase P correlates with per-swab viral copy number.