The stepwise multivariate model analysis identified age, history of allergy, atopy, or asthma, presence of autoimmune disorders, other medications, sex, days since the first and second vaccinations, MCV, LYMPH, IgG titers post first vaccination, naïve% in CD8+ T cells, and spike-specific CD4+ T cells after the first and second vaccinations as independent predictors of peak IgG titers (Adjusted R-squared; Full model: 0.289, Selected model: 0.344) (Table 5). This evidence concerns the gene CD4 and allergic disease.