In the current systematic review, the highest-quality evidence comes from large studies in England and Spain. The nationally representative evidence included serologic surveys from more than 365,000 people in England and more than 61,000 in Spain. When analyzed separately, about the same proportion of asymptomatic cases emerged: 32.4% in England and 33% in Spain. 

“It was really remarkable to find that nationwide antibody testing studies in England and Spain — including hundreds of thousands of people — produced nearly identical results: about one third of the SARS-CoV-2 infections were completely asymptomatic,” said Oran, a researcher at Scripps Research Translational Institute in La Jolla, California.

Cite this: More Than One Third of COVID-19 Infections Are Asymptomatic: Review – Medscape – Jan 25, 2021. — https://www.medscape.com/viewarticle/944662?src=rss#vp_1