Statistical analysis
All statistical analyses were performed using GraphPad Prism (v.9.0; La Jolla, CA, USA). The Shapiro-Wilk test was performed to evaluate the normality of the data. Differences between the groups, including poultry farm personnel, positive, and negative controls, were determined using Kruskal-Wallis test with the Dunn’s multiple comparisons. The alternative parametric test, one-way ANOVA, was implemented if data were normally distributed. In this case, Tukey’s test was performed as a post hoc comparison. The correlation between antibodies was tested using Spearman correlation. Heatmaps were created using GraphPad Prism (v.9.0; La Jolla, CA, USA). Spearman rank correlation matrix generated by Morpheus matrix visualization software (https://software.broadinstitute.org/morpheus/). Two-tailed Mann–Whitney U test was used to compare differences between the groups (non-hospitalized vs. hospitalized COVID-19 patients and vaccine implementers vs. poultry workers) for IgG ratios. For all statistical analyses, a probability level of P <0.05 was accepted as statistically significant.