First, to describe SARS-CoV-2 T cell and antibody responses in a prospective cohort of healthcare workers that suffered from mild to moderate COVID-19 approximately one year ago. Second, to assess COVID-19 vaccine-induced immune responses in these prior-infected individuals.

SARS-CoV-2-specific T cell and anti-SARS-CoV-2-Spike-RBD immunoglobulin G (IgG) responses in blood were determined before COVID-19 vaccination with mRNA-1273, BNT162b2, Ad26.CoV2-S or ChAdOx1-S, two weeks after first vaccination, and after second vaccination.

55 prior SARS-CoV-2 infected and seroconverted individuals were included. S1-specific T cell responses and anti-RBD IgG were detectable one year post SARS-CoV-2 infection: 24 spot-forming cells per 10⁶ peripheral blood mononuclear cells (SFCs/10⁶ PBMCs) after S1 stimulation and anti-RBD IgG concentration of 74 (IQR 36–158) IU/mL. Responses after the first and second vaccination were comparable with S1-specfic T cell responses of 198 (IQR 137–359) and 180 (IQR 103–347) SFCs/10⁶ PBMCs, and IgG concentrations of 6792 (IQR 3386–15,180) and 6326 (IQR 2336–13,440) IU/mL, respectively. These responses retained up to four months after vaccination.

Both T cell and IgG responses against SARS-CoV-2 persist for up to one year after COVID-19. A second COVID-19 vaccination in prior-infected individuals did not further increase immune responses in comparison to one vaccination.