From February 1st until March 24th, 2021, the SCOPE study measured the proportion of residents and staff members in Belgian nursing homes (NH) that had anti-SARS-CoV-2 antibodies (seroprevalence). In total, 1,572 residents and 1,253 staff members from 69 NHs in Belgium were tested for the presence of SARS-CoV-2 antibodies by a point-of-care rapid test, and responded to a COVID-19 related questionnaire. At the first testing moment (five bimonthly follow-up testing moments are scheduled), we observed the following:Between February 1st and March 24th, 2021, during the ongoing SARS-CoV-2 vaccination campaign, 69% (95% CI: 63%-74%) of residents and 80% (95% CI: 76%- 83%) of staff in Belgian nursing homes had anti-SARS-CoV-2 antibodies. At the time of testing 96% of the residents received at least one vaccination dose and 68% were fully vaccinated. For staff this data were respectively 85% and 48%. So, although more residents than staff were vaccinated at the moment of testing, seroprevalence was lower among residents than among staff. At least one day after receiving one dose of a COVID-19 vaccination, 52% of residents tested positive for anti-SARS-CoV-2 antibodies and 77% tested positive at least one day after receiving two doses. Among staff these findings were higher, being respectively 75% and 98%. The proportion of residents and staff with antibodies after vaccination was higher among those who reported a previous SARS-CoV-2 infection than among those without a self- reported previous infection. ; SCOPE