Glycan switch may explain why SARS-CoV-2 causes such variable symptoms Researchers in Portugal have provided evidence that might explain why infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes mild or even asymptomatic illness in some individuals, but severe coronavirus disease 2019 (COVID-19) in others. Salome Pinho from the University of Porto and colleagues showed that circulating T cells exhibit a specific “glycan switch” following infection with SARS-CoV-2 and that this switch is more pronounced in asymptomatic versus symptomatic individuals. The researchers say this change in the T cell glycosylation profile appears to be triggered by a serum inflammatory factor, the identification of which could lead to a potential new biomarker and therapeutic target.