Multiplexed Salivary miRNA Quantification for Predicting Severe COVID-19 Symptoms in Children Using Ligation-RPA Amplification Assay

Most children with SARS-CoV-2 have mild or asymptomatic symptoms, but some develop severe complications. Early identification of high-risk cases is crucial for timely intervention. Alterations in salivary microRNA (miRNA) levels serve as biomarkers for severity prediction. However, a rapid, non-invasive method is needed to quantify miRNA level changes as an alternative to sequencing. Here, we developed a highly specific and sensitive ligation-recombinase polymerase amplification (RPA) assay for quantifying severe and non-severe miRNAs on a portable platform. The assay begins with a miRNA-templated annealing and ligation-RPA reaction of miR-1273, miR-296, and miR-29. We quantified 100 pM to 1 fM, resolving 1 fM, with 100% specificity. Next, we validated portable extraction against benchtop extraction, achieving R-square > 0.85 and r > 0.92 in clinical samples. Finally, testing 154 clinical samples revealed severe miRNA downregulation compared to non-severe cases. The assay achieved high diagnostic accuracy with an AUC of 0.98. This platform enables informed clinical decisions and optimizes resources, especially in resource-limited settings.