Long COVID and type I IFN signature in working-age adults. A cross-sectional study

To investigate relevant biomarkers that might aid in the diagnosis and monitoring of long COVID (LC), an analysis of IFN-α, IFN-β, ISG15, and ISG56 transcripts was performed by Real-Time PCR among people of working age who had been infected with SARS-CoV-2 one year prior to the study [LC and non-long COVID (NLC)]. Despite no differences in the transcript levels of IFN-α, IFN-β, ISG15, and ISG56 between LC and NLC, higher IFN-β mRNA levels were observed among LC compared to NLC individuals who were hospitalized for more than 10 days during acute SARS-CoV-2 infection. Moreover, previously SARS-CoV-2 infected participants that did not require respiratory support and developed LC exhibited higher levels of IFN-α and IFN-β compared to NLC with the same clinical characteristics. These results highlight that SARS-CoV-2 infection leads to changes in peripheral innate immune pathways, which could have implications for the development of LC.