The media has made it seem that asymptomatic cases are weird; in fact, it is estimated 72% of polio cases were asymptomatic. In the past I saw one study of influenza in one particular year where they estimated about 3 in 4 cases were asymptomatic (can’t find the link at the moment).
The first long-term seroprevalence study of residents in Wuhan, China, has found that 6.9% of people in the city had antibodies against COVID-19 in April 2020, and 82% of these people had an asymptomatic infection. Additionally, 40% of people with antibodies developed neutralising antibodies, and these levels did not decrease between April and October-December 2020. The results are published in an observational study of 9,542 people in The Lancet.