Mass-Standardised IgG Response to Fourteen SARS-CoV-2 Spike Protein variants and Antibody Subclass analysis for IgG subclasses and IgE for a Long COVID Patient Cohort

A multivariant total subclass analysis has been performed for a control cohort (n=15) and a long COVID patient cohort (n=15) measuring the IgG1, IgG2, IgG3, IgG4 and IgE response to the following 14 variants of SARS-CoV-2: Wuhan, Alpha, Delta, BA.1, BA.2, BA.5, EG.5.1, XBB.1.5, BA.2.75, CH.1.1, BA.2.12.1, BQ.1.1, JN.1, and KP.3. Significant differences (p < 0.05 and p < 0.005) between concentrations of IgG subclasses by variant were found in 24% of variants and in mean-normalised distributions. The medians of the mean-normalised distributions were significantly lower for IgG1 (p < 0.05) in long COVID patients compared with controls, and significantly higher (p < 0.005) for levels of IgG3, IgG4 and IgE for long COVID patients. A preliminary diagnostics classification analysis performed by variation of the mean-normalised upper and lower percentiles symmetrically for IgG3 showed a long COVID diagnostic sensitivity of 80%, and specificity of 80% for the 60th percentile threshold of the control cohort. Three types of long COVID can be identified: patients with at least one variant below the threshold (hypo-immune), patients with at least one variant above the threshold (hyperimmune) and patients with IgG3 levels within the reference range. The multivariant subclass spectrum indicates IgG4 and IgE elevations due to potential chronic antigen exposure from persistent virus or autoimmunity and may indicate potential therapeutic interventions.