https://www.forbes.com/sites/isabeltogoh/2020/04/06/china-thought-it-had-beaten-coronavirus-but-new-and-asymptomatic-cases-are-cropping-up/
"CDC director Dr Robert Redfield estimates that as many as 1 in 4 people with coronavirus are asymptomatic, i.e. will not show outward symptoms, but can still pass the virus on without knowing."