PROTECTIVE ROLE OF ANTI-S IGG AGAINST SARS-COV-2 DURING THE OMICRON VARIANT WAVE AMONG HEALTHCARE WORKERS: RESULTS FROM TWO LARGE ITALIAN UNIVERSITY HOSPITALS – ORCHESTRA PROJECT.

Introduction Vaccination is effective against SARS-CoV-2 infection. However, the role of anti-S IgG (AS) in preventing infection is still unclear. Aim of this study was to understand whether health workers (HW) with high AS titers sustained a lower risk of infection across the Omicron variant (OV) period. Methods Within the framework of the ORCHESTRA European project, 3,565 HW from Padova and Verona cohorts, who had at least one AS titration after booster dose, were included. A stratified survival analysis was performed, considering as infected by OV those HW with a positive RT-PCR test between December 2021 and June 2022. Results Older age groups (40-49 Hazard Ratio=0.76; CI: 0.64-0.91; p=0.003; 50-59 HR=0.79; CI: 0.67-0.95; p=0.009; >60 HR=0.75; CI: 0.59-0.96, p=0.02) had a lower risk of infection. Previous infected HW had a diminished risk too, although only infections before the first dose reached significance (HR=0.70; CI: 0.54-0.89; p=0.004). The risk reduction was about 18% among HW who had antibody titer above the 80th percentile (HR=0.82; CI 0.71-0.95; p=0.007). Discussion Our data showed that older and previously infected HW sustained lower risk of infection during the OV wave. The scant research on AS titer role against OV shows that higher AS levels ensure stronger protection. Our study seems to support these findings. However, this effect is limited and not usable to exclude from further booster doses the HW with high antibody titers. Conclusion High AS titer against SARS-CoV-2 showed a protective, albeit mild, role against infection across OV period.