Rapid Rise of S-Gene Target Failure and the UK variant B.1.1.7 among COVID-19 isolates in the Greater Toronto Area, Canada

A novel variant of SARS-CoV-2, B.1.1.7, originally discovered in the United Kingdom (UK), is rapidly overtaking other strains around the globe. In certain assays, absence of detection of the S-gene target, also known as S-gene target failure (SGTF) can be a sensitive surrogate of B.1.1.7. We analyzed daily counts of SGTF among samples from Dynacare Laboratory Ontario (which draws samples from the Greater Toronto Area) and resulted between December 16, 2020 and February 3, 2021. We identified 11,485 positive COVID-19 tests, of which 448 had SGTF (3.9%). The estimated prevalence of SGTF rose from 2.0% on December 16 to 15.2% on February 3 (1.8-fold weekly increase, 95%CI: 1.5, 2.2). The estimated reproduction number for SGTF cases was 1.17 (95%CI: 0.94 to 1.46), while the reproduction number for non-SGTF cases was 0.82 (95%CI: 0.65 to 1.01); the relative reproduction number was 1.44 (95%CI: 1.03, 1.99). 59 samples were sent for confirmatory testing, of which 53 (90%) were identified as B.1.1.7 using whole genome sequencing or found to have the N501Y mutation. In order to pre-emptively plan and implement public health measures to control COVID-19 now and through the spring, accurate and up-to-date early warning systems for new variants, including B.1.1.7, are essential across North America and the globe.