Multiplexed RT-qPCR to screen for SARS-COV-2 B.1.1.7, B.1.351, and P.1 variants of concern v3

Abstract

With the emergence of SARS-CoV-2 variants that may increase transmissibility and/or cause escape from immune responses, there is an urgent need for targeted molecular surveillance methods. While sequencing is the gold standard, it cannot always be immediately scaled or implemented in some settings to detect variants when their frequencies are low. The Applied Biosystems TaqPath COVID-19 assay (ThermoFisher), a PCR test, was discovered to have a distinct signature (spike gene target failure, [SGTF]) when testing viruses containing the Δ69/70 HV deletion, like the B.1.1.7 variant first detected in the UK. However, a sample with a SGTF is not definitive for B.1.1.7, and cannot detect other variants of concern that lack the Δ69/70 HV deletion, such as B.1.351 detected in South Africa and P.1 recently detected in Brazil. We developed a multiplexed RT-qPCR assay that can detect all three variants by targeting the Δ3675-3677 SGF deletion in the ORF1a gene, which has not yet been widely detected in other SARS-CoV-2 lineages. Furthermore, by also targeting the Δ69/70 HV deletion in the spike gene, our assay can differentiate B.1.1.7 from B.1.351 and P.1. Finally, we include the CDC N1 primer and probe set in our multiplexed assay as a control to ensure that target failures are likely due to the presence of the ORF1a and/or spike deletions and that there is sufficient virus RNA for sequencing confirmation. Our multiplexed RT-qPCR assay can be rapidly scaled to support SARS-CoV-2 variant surveillance.