Figure 1.

Conceptual decision tree for distinguishing between an infection- and vaccine-induced humoral immune response. Serosurvey investigators should collect all data simultaneously (eg, deploy anti-S and anti-N assays together) before applying the conceptual decision tree. Assays measuring total antibodies or IgG can be used. Anti-RBD assays can be used in place of anti-S assays. A past diagnosis, if present, can support the conclusion that an individual should be assigned to group A or C. This decision tree is only applicable for S-targeting vaccines. Abbreviations: IgG, immunoglobulin; N, nucleocapsid protein; RBD, receptor-binding domain; S, spike glycoprotein.