SARS-CoV-2 antigen-specific IgG levels in poultry farm personnel, COVID-19 patients and pre-COVID-19 controls
We determined the levels of serum specific IgG for the SARS-CoV-2 antigens S1, RBD, S2, and N by ELISA. S1-specific IgG levels were significantly higher in COVID-19 patients compared to poultry farm personnel and pre-pandemic control samples (Figure 1A). RBD-specific IgG levels of COVID-19 patients were also higher than those of poultry farm personnel and pre-pandemic control samples (Figure 1B). Likewise, S2- and N-specific IgG levels were the highest in COVID-19 patients when compared to poultry farm personnel and pre-pandemic control samples (Figure 1C,D; Table S7). Hospitalized COVID-19 patients exhibited significantly higher S1-, RBD-, S2- and N-specific IgG levels than non-hospitalized COVID-19 patients (Figure S1A-D). The heatmap (Figure 1E) illustrates that all of the COVID-19 patients had high levels of IgG against all four SARS-CoV-2 antigens. As an interesting finding, the levels of S1-, RBD- and N-specific IgG were significantly higher in poultry farm personnel compared to the pre-pandemic control group (P <0.05), while S2-specific IgG levels were not statistically different. A fraction of the poultry farm personnel (VI20, VI23, VI27, VI29, VI30, VI34, VI36, VI37, VI38, VI39, PW9) showed higher specific antibody levels than the pre-pandemic control. 10 out of these 11 poultry farm personnel were the vaccine implementers (90.91%) and one was a poultry worker (9.09%) (Figure 1E). Only one sample (VI17) exhibited the IgG OD ratio of >0.6 for all SARS-CoV-2 antigens.
The OD ratios of S1-, RBD-, S2-, and N-specific IgG were significantly higher in COVID-19 patients than in poultry farm personnel and the pre-pandemic control group (P <0.0001) (Figure 1A-D). There was no difference between vaccine implementers and poultry workers regarding S1-, RBD-, S2-, and N-specific IgG OD levels (Figure S1E-H).
Concerning the individuals which exhibited OD values of S1- and RBD-specific IgG above the threshold at 0.1, the majority of these individuals were vaccine implementers (33.33% and 38.46%, respectively) compared to poultry workers (21.43% and 14.29%, respectively). However, the percentages of poultry workers were predominant for S2- and N-specific IgG (71.43% and 78.57%, respectively), as shown in Figure 1F.