RESUMEN
Among new vaccine technologies contributed to the control of the COVID-19 pandemic, ChAdOx1 nCoV-19, a chimpanzee adenovirus (ChAd)-vector vaccine expressing the SARS-CoV-2 spike protein, could be administered globally owing to its low production cost and lack of a requirement for frozen storage. Despite its benefits, most recipients have reported immediate inflammatory reactions after the initial dose vaccination. We comprehensively examined the immune landscape following ChAdOx1 nCoV-19 vaccination based on the single-cell transcriptomes of immune cells and epigenomic profiles of monocytes. Monocyte and innate-like activated T cell populations expressing interferon-stimulated genes (ISGs) increased 1 day post-vaccination with appearance of distinct subtype of ISG-activated cells, returning to baseline by day 14. Pre-treatment with oral corticosteroids effectively curtailed these ISG-associated inflammatory responses by decreasing chromatin accessibility of major ISGs, without hampering vaccine immunogenicity. Our findings provide insights into the human immune response following ChAd-based vaccination and propose a method to reduce inflammatory side effects.