Delhi's sero-prevalence study has found that 23.48 per cent of the people have been affected by COVID-19 in the city, which has several pockets of dense population, the Union Health Ministry said on Tuesday. The study, which was conducted from June 27 to July 10 by the National Center for Disease Control (NCDC) in collaboration with the Delhi government, also indicated that a large number of infected persons remain asymptomatic, it said.