“Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a potentially long incubation period and spreads opportunistically among those who are unaware they are infected. Asymptomatic COVID-19 cases are those that do not develop symptoms for the duration of infection, whereas presymptomatic cases develop symptoms later in the course of infection, but both are crucial drivers of transmission. …”

https://science.sciencemag.org/content/371/6535/1206