ABSTRACT
Antibody profiling of vaccinated versus naturally infected individuals is important in evaluating immunity and aiding diagnosis and booster strategies. This study measured antibodies against different antigen targets in healthcare workers (HCW) who have been fully vaccinated with mRNA vaccines, recovered from natural infection, or patients during active infection. All vaccinated individuals were positive for anti-RBD, anti-S1, and anti-S2 antibodies. The median index and interquartile range (IQR) by the Atellica IgG assay were 179 and 140-291 respectively. Among the different antigen targets within the Bioplex assay, the levels of anti-RBD were highest (median >3200 U/mL; IQR >3200 to >3200 U/mL), followed by anti-S1 (median 2132 U/mL; IQR 1649->3200 U/mL) and anti-S2 (median=42 U/mL; IQR=24-76 U/mL). The non-vaccinated recovered cohort showed 90% seropositivity (median index >10; IQR 3.6->10) by Atellica total antibody, 73% by Atellica IgG (median index 3.3; IQR 0.9-9.4), 84% by Bioplex anti-RBD (median 62; IQR 12-269 U/mL), 77% by Bioplex anti-S1 (median 45; IQR 10-83 U/mL), 37% by Bioplex anti-S2 (median 7; IQR 1-12 U/mL), and 79% by Bioplex anti-nucleocapsid (median 69; IQR 20-185U/mL) respectively. The active infection cohort exhibited a similar pattern as the recovered cohort. About 88% and 78% of the recovered and active infection cohort produced both anti-spike and anti-N antibodies with Anti-S1/anti-N ratios ranging from 0.07-16.26. In summary, fully vaccinated individuals demonstrated an average of 50-fold higher antibody levels than naturally infected unvaccinated individuals with immune reactivity strongly towards RBD/S1 and a weak response to S2. The results support vaccination regardless of previous COVID-infection status.
