Table 3 WGS cross-validation results for all three rounds organised in 2021. Results are considered correct if the receiving laboratory reports results in concordance with the sending laboratory. Lab 15, not part of the convention, did not participate to the third cross-validation round, organised in October 2021. Lab 6 was unable to obtain a result for 1/3 cross-validation samples for the first two rounds. In the first case they voluntarily tested a new panel for which they obtained the maximum score; as an action for the second round, the failed sample was sequenced by the NRC, who was also unable to type the sample. Therefore, it was assumed that RNA degradation had occurred during transport from the sending laboratory to the NRC. For round one, lab 17 reported two samples as ‘undetermined’ due to low cDNA amplification. For the second round, lab 10 could not obtain a result for one cross-validation sample. The laboratory indicated this problem occurred when UTM samples were extracted using the extraction kit from the federal platform laboratories (note that federal platform laboratories only routinely test samples taken in virus inactivating medium). Lab 9 was unable to report a result for two cross-validation samples due to low RNA concentrations

From: Nationwide quality assurance of high-throughput diagnostic molecular testing during the SARS-CoV-2 pandemic: role of the Belgian National Reference Centre