ORIGINAL RESEARCH article
Front. Immunol.
Sec. Vaccines and Molecular Therapeutics
Volume 16 - 2025 | doi: 10.3389/fimmu.2025.1636629
Immune Memory Reactivation and T Cell Dynamics Following 12-Month Homologous CoronaVac Booster: A Longitudinal Cohort Study
Provisionally accepted
- Beijing Center for Disease Prevention and Control (Beijing CDC), Beijing, China
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Background: Inactivated COVID-19 vaccines exhibit more rapid declines in antibody levels than other vaccine platforms, likely owing to transient antigen exposure and limited germinal center persistence. Moreover, although homologous boosting effectively restores humoral immunity, concerns persist regarding potential T cell exhaustion with repeated antigen exposure. We evaluated the effectiveness of delayed homologous CoronaVac booster immunization in reactivating immune memory.Methods: A prospective longitudinal cohort study was conducted with 83 healthy adults who received two CoronaVac vaccine doses (14-day interval) and a homologous booster shot after 12 months. Peripheral blood samples were collected 0, 3, 7, 10, and 14 days after booster vaccination. Neutralizing antibodies were analysed using live-virus microneutralization assays. Anti-receptor-binding domain immunoglobulin subclasses (IgG1, IgG2, IgG3, IgG4) were detected using enzyme-linked immunosorbent assay. Cytokine secretion (interferon [IFN]-γ/interleukin [IL]-2/IL-4/IL-5) was assessed using enzyme-linked immunospot assay. T cell polarization and exhaustion markers (T-bet/GATA3 and CD69/CTLA-4/PD-1) were evaluated using flow cytometry. Results: The geometric mean titer of neutralizing antibodies reached 254.5 on day 14. The initial immune response was dominated by IgG3, which subsequently shifted to IgG1. A significant Th1-type cellular immune response was characterized by increased IFN-γ and IL-2 secretion, and upregulated T-bet expression. Transient CD69+ T cell activation occurred between days 3 and 10 without sustained PD-1 and CTLA-4 elevation. Conclusions: Delayed homologous CoronaVac booster immunization effectively reactivates immune memory, facilitated by Th1 polarization and transient T cell activation, which do not result in T cell exhaustion. These findings suggest the potential application of long-interval immunization strategies against COVID-19.
Keywords: SARS-CoV-2 inactivated vaccine, Homologous boosting, neutralizing antibodies, t cell exhaustion, Th1 polarization
Received: 28 May 2025; Accepted: 28 Jun 2025.
Copyright: © 2025 Song, Chen, Bai, Lv, Wang, Zhang, Wu and Zhao. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Jiang Wu, Beijing Center for Disease Prevention and Control (Beijing CDC), Beijing, China
Wei Zhao, Beijing Center for Disease Prevention and Control (Beijing CDC), Beijing, China
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