SARS-CoV-2 and RSV external quality assessment on molecular detection and variant typing in European expert laboratories in 2025

We herein report on the fourth SARS-CoV-2 wet-lab external quality assessment (EQA) and the second organized by the AURORAE consortium to assess the diagnostic capabilities of European expert public health laboratories. Diagnostic capabilities were investigated regarding SARS-CoV-2 and, for the first time, respiratory syncytial virus (RSV) groups A and B. A 10-sample panel containing various SARS-CoV-2 variants, RSV lineages, a common cold coronavirus, and a negative control was produced and validated. Participants were invited by the European Centre for Disease Prevention and Control (ECDC) and asked to submit results and assay details via electronic forms. Thirty-seven laboratories from 32 European countries participated. All panel samples were identified correctly via molecular detection by 23 participating laboratories (23/37; 62%). Commercial assays were used most often (23/37; 62%), in comparison to in-house assays (14/37; 38%), or a combination of both (8/37; 22%). RSV groups were correctly determined by 20 laboratories (20/37; 54%). The optional task of SARS-CoV-2 variant typing was performed by 20 laboratories using next-generation sequencing. Thirteen laboratories successfully generated SARS-CoV-2 sequences. Six laboratories performed optional RSV sequencing, with only two obtaining sequences. The current and previous EQAs show that molecular detection of SARS-CoV-2 within Europe has improved over time and is now at a consistently high level. Molecular detection of RSV samples with low viral load was challenging, as was lineage identification for low-concentration specimens. Routine monitoring of diagnostic and surveillance assays via EQAs remains key to maintaining rapid and long-lasting public health laboratory response systems.IMPORTANCEExternal quality assessments (EQAs) are essential for ensuring reliable and consistent diagnostic testing. They provide an objective way to evaluate laboratory performance, identify weaknesses, and drive improvements, as well as ensuring compliance with accreditation standards. Furthermore, participating in EQAs strengthens the contributions to public health disease surveillance and threat detection on national and transborder scales. During the SARS-CoV-2 pandemic, EQAs were vital for maintaining accuracy in the setting of increasing testing demands and emerging variants. Broadening of diagnostic testing to a wider panel of viruses, including respiratory syncytial virus (RSV), requires continuous performance monitoring to ensure accuracy and reliability. Ongoing development of vaccines and therapeutics, which may drive the emergence of new mutations, further underscores the need for regular evaluation of test effectiveness. By standardizing methods and reducing errors, EQAs ensure trustworthy and comparable results across laboratories. Regular participation in EQAs strengthens molecular diagnostics and variant surveillance.