We tested seroprevalence of open reading frame 8 antigens to infer the number of unrecognized SARS-CoV-2 Omicron infections in Hong Kong during 2022. We estimate 33.6% of the population was infected, 72.1% asymptomatically. Surveillance and control activities during large-scale outbreaks should account for potentially substantial undercounts.
Keywords: COVID-19; China; Hong Kong; ORF8 antigen; SARS-CoV-2 Omicron variant; infection attack rate; respiratory infections; viruses; zoonoses.