Figure 4.

Anti-RBD IgG levels and neutralizing antibody titres stratified according to isolation status among HCWs infected with Omicron. Samples having a similar high viral load (≥6 log₁₀ cp/10⁶ cells) were selected. A chemiluminescence immunoassay (CLIA) was performed in order to determine anti-RBD IgG levels, expressed here in binding antibody unit/mL (BAU/mL) and stratified according to culture status (A). The dotted line represents the threshold of positivity (≥21.8 BAU/mL). A 50% plaque reduction neutralization test (PRNT₅₀) was conducted to determine the neutralizing antibody titre of each sample against the live Omicron variant and stratified according to culture status (B). The dotted line represents the threshold of positivity (a titre ≥ 20). For both experiments, box plots represent the median [IQR] for each parameter and before-and-after scatter plots represent the evolution of the parameter for each patient individually. Comparisons were made using the Mann–Whitney U-test. **p < 0.01.