Immune Responses Against SARS-CoV-2 in Previously SARS-CoV-2-Infected Individuals after Receiving a Single Dose of CoronaVac or ChAdOx-1 Vaccine

Abstract

Background: Although infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) could induce natural immunity, previously infected individuals were suggested to have additional vaccination to enhance immune responses against the new variants of concern (VOCs). In this study, we determined the effects of a single dose of inactivated vaccine and viral vector-based vaccine on the neutralizing antibody (NAb) and T cell responses against the wild type (WT) and VOCs in the post-infection individuals. Materials and Methods: The levels of NAb and specific T cell responses against the WT and VOCs of the previously infected individuals were determined before and after vaccination with a single dose of CoronaVac (CoVac) or ChAdOx-1 (ChAd) vaccine. Results: Eighteen subjects, with nine participants in each vaccination group, were recruited in this study. The CoVac group was significantly older (53.3±12.8 vs. 34.4±14.0 years, P=0.009) and had shorter disease-vaccination time (111.0 vs. 186.0 days, P <0.001) than the ChAd group. Before vaccination, both groups had median NAb against WT, Alpha, Beta, and Delta variants, but not Omicron BA.4 and.5 variants, above the detection threshold. After vaccination, the NAbs and the CD4 and CD8 T-cell responses against the tested variants were demonstrated. However, the NAb in the CoVac arm was lower than in the ChAd arm. In contrast, the CoVac vaccine-induced T-cell responses are better than the ChAd vaccine. Conclusion: In post-SARS-CoV-2 infection, ChAd vaccination induced a better antibody response, but the CoVac vaccine induced greater T-cell responses. Vaccination is valuable in boosting immunity, particularly against some VOCs, in individuals with prior SARS-CoV-2 infection. © 2025 by The Korean Society of Infectious Diseases, Korean Society for Antimicrobial Therapy, The Korean Society for AIDS, and Korean Society of Pediatric Infectious Diseases.