There have been limited data on the risk of onward transmission from individuals with Omicron variant infections who return to work after a 5-day isolation. To evaluate the risk of transmission from healthcare workers (HCWs) with Omicron variant who returned to work after a 5-day isolation and the viable-virus shedding kinetics. This investigation was performed in a tertiary care hospital, Seoul, South Korea. In a secondary transmission study, we retrospectively reviewed the data of HCWs confirmed as COVID-19 from March 14th to April 3rd, 2022 in units with five or more COVID-19-infected HCWs per week. In the viral shedding kinetics study, HCWs with Omicron variant infection who agreed with daily saliva sampling were enrolled between February and March, 2022. Of the 248 HCWs who were diagnosed with COVID-19 within 5 days of the return of an infected HCW, 18 (7%) had contact with the returned HCW within 1–5 days after their return. Of these, nine (4%) had an epidemiologic link other than with the returning HCW, and nine (4%) had contact with the returning HCW, without any other epidemiologic link. In the study of the kinetics of virus shedding (N = 32), the median time from symptom onset to negative conversion of viable virus was four days (95% confidence interval: 3–5). Our data suggest that the residual risk of virus transmission after 5 days of isolation following diagnosis or symptom onset is low.