Figure 1.

Participant flow diagram. A confirmed positive serological result was defined as an initial positive result (antinucleocapsid or antispike antibody [Ab] result), followed by confirmation with a second positive serological result using a different target (antinucleocapsid, antispike, or neutralizing Abs). A positive unconfirmed serological result was defined as an isolated positive antinucleocapsid or antispike Ab result (ie, a negative result with confirmatory testing) in the absence of reverse-transcription polymerase chain reaction (RT-PCR) positivity. Prevalent coronavirus disease 2019 (COVID-19) cases were defined as those in participants with a positive RT-PCR or a confirmed positive serological result at baseline, and incident COVID-19 cases as those in participants with a positive RT-PCR or a confirmed positive serological result at any subsequent visit.