“This study looking at PCR test data from nearly 10 million residents in Wuhan city found that not a single one of those who had been in close contact with an asymptomatic individual tested positive. Asymptomatic people do not spread COVID-19.”  

Cao, S., Gan, Y., Wang, C. et al. Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China. Nat Commun 11, 5917 (2020). https://doi.org/10.1038/s41467-020-19802-w