In the present study, we compared and combined QFN and AIM assays, and analyzed memory CD4+ and CD8+ T-cell responses along with anti-S1 and anti-N antibody responses, in order to more exhaustively evaluate the immunological memory persisting in immunocompetent unvaccinated individuals with prior symptomatic infection documented up to 2 years earlier (late convalescents), compared to fully vaccinated asymptomatic donors (vaccinees). This evidence concerns the gene CD4 and infection.