Saliva—Friend and Foe in the COVID-19 Outbreak

The coronavirus disease 2019 (COVID-19) outbreak, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a global ongoing pandemic. Timely, accurate and non-invasive SARS-CoV-2 detection in both symptomatic and asymptomatic patients, as well as determination of their immune status, will facilitate effective large-scale pandemic control measures to prevent the spread of COVID-19. Saliva is a biofluid whose anatomical source and location is of particularly strategic relevance to COVID-19 transmission and monitoring. This review focuses on the role of saliva as both a foe (a common mode of viral transmission via salivary droplets and potentially aerosols) and a friend (as a non-invasive diagnostic tool for viral detection and immune status surveillance) in combating COVID-19.