Finding non-invasive methods to detect the SARS-CoV-2 virus has been essential for rapid self-testing during the pandemic. This study compared gingival crevicular fluid (GCF), taken by swabbing the gums, to blood samples from patients in the ISARIC4C UK study. It was shown that GCF taken from the gums can detect the virus, and higher levels of SARS-CoV-2 antibodies in the GCF in the early acute phase of the illness are linked to more severe COVID-19 infections.