Researchers remain perplexed as to why some patients infected with SARS-CoV-2, the virus responsible for COVID-19, remain asymptomatic while other patients develop severe disease symptoms. This question is once again at the front of mind as the Delta variant spreads across the country. In a new retrospective study, researchers at the Medical University of South Carolina (MUSC) discovered a specific and sensitive biomarker in blood samples that predicts which patients will develop COVID-19 symptoms. Their results, published online on July 9 in Scientific Reports, show that reduced levels of a specific lipid, sphingosine, are significantly associated with developing COVID-19 symptoms. Conversely, elevated levels of sphingosine, as well as a protein involved in its production, acid ceramidase (AC), are associated with asymptomatic infections.