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Study Compares PCR Cycle Thresholds for Wild Type, Variants of SARS-CoV-2

For a paper appearing in PLOS One, a team from Germany and Austria examines cycle threshold differences between wild-type SARS-CoV-2 and mutant versions of the coronavirus, including variants of concern such as Alpha and Beta. The researchers retrospectively looked at 1,873 samples that tested positive for SARS-CoV-2 by PCR, including more than 1,000 wild type samples, 845 samples containing the Alpha variant and 15 Beta variant-containing samples. "Cycle threshold (Ct) values that are generated in a real-time polymerase chain reaction (PCR) are a way of estimating the virus concentration in a sample semi-quantitatively. This roughly reflects the viral load in the patient's material and could allow conclusions to be drawn about the infectiousness of a patient," the authors write, noting that results so far suggest that effect size calculations "would allow an estimation of the magnitude of difference in Ct values and of their true meaning in vivo.