PA-785 Characterization of anti-SARS-CoV-2 humoral immunity among health care workers in hospitals from the islands of Santiago and São Vicente, Cabo Verde

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Background Health Care Workers (HCW) faced a high risk of exposure to SARS-CoV-2. In the present study, we described the presence and duration of anti-S and anti-N IgG antibodies against SARS-CoV-2 among HCW to evaluate the immunity response induced by either SARS-CoV-2 infection or COVID-19 vaccination. Methods Case-cohort study of 465 HCW from hospitals from the islands of Santiago and São Vicente, conducted in 2021, of which 217 were cases (SARS-CoV-2 infection) and 248 controls (no SARS-CoV-2 infection). Study participants were followed-up until 6 months after recruitment for longitudinal analysis of antibody dynamics, independently of SARS-CoV-2 vaccination status. ELISA test for anti-N and anti-S1 SARS-CoV-2 IgG antibodies were performed on serum samples using collected at baseline (T0) and at 6 months (T6). Among vaccinated participants, these two time points corresponded to a mean time from vaccination of 115 (SD: 60 days) and 350 days (SD: 74 days) respectively. Results Of the 396/465 (85%) tested for anti-SARS-CoV-2 antibodies at T0, 36% (n=66/185) of cases and 12% of controls (n=26/211) were positive for anti-N. Among the vaccinated at T0 165/166 (96%) cases and 200/205 (97%) controls were positive for anti-S1. The anti-S1 among the case and control group remained high at T6, with 177/179 (99%) cases and 197/198 (99%) controls of HCW tested at 6 months being positive. Among 250 (67%) vaccinated, who were anti-N negative at T0-,115(32%) remain negative at T6. Conclusion These findings showed that only 31% of cases had anti-N. The results also showed positive results for IgG anti-N in HCW without previous SARS-CoV-2 infection, which could be considered asymptomatic cases. Most vaccinated participants had Anti-S after vaccination and they remained high during the 6 months of follow-up. Nonetheless, at least (65/354) had a new infection (32 cases, 33 controls). Funding: EDCTP (RIA2020EF-3049)

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