Question to the Department of Health and Social Care:

To ask the Secretary of State for Health and Social Care, what assessment his Department has made of the effectiveness of Polymerase Chain Reaction tests after 45 cycles.

In August 2020, a study performed and published by Eurosurveillance looked at a selection of cases to identify samples that were Polymerase Chain Reaction (PCR) positive for COVID-19 and which had infectious virus. It found the PCR cycle threshold (Ct) values correlate strongly with infectious virus, meaning when there is more infectious virus the Ct value is lower. The probability of culturing virus declines to 8% in samples with Ct?more than?35 and to 6% 10 days after symptom onset. This would be lower for Ct with more than 45 cycles.

The Eurosurveillance study is available at the following link:

https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.32.2001483?crawler=true