Status of Humoral and Cellular Immune Responses within 12 Months Following CoronaVac Vaccination Against COVID-19

Background: Understanding immune memory to COVID-19 vaccines is critical for the design and optimal vaccination schedule for curbing the COVID-19 pandemic. Here, we assessed the persistence of humoral and cellular immune responses for 12 months after two-dose CoronaVac. Methods: Participants aged 18–59 years received two doses of 3 μg CoronaVac 14 days apart, and blood samples were collected before vaccination (baseline) and at 1, 3, 6, and 12 months after the second shot. Humoral responses of specific antibodies and neutralising antibodies were measured by using chemiluminescent immunoassay and wild-type SARS-CoV-2 microneutralisation assay, respectively. Cellular responses were measured by immunospot-based and intracellular cytokine staining assays. This trial is registered with ClinicalTrials.gov, NCT05072496. Findings: Total 150 participants were enrolled, and 136 of them completed the study through the 12-month endpoint. At 1 month after vaccination, binding and neutralising antibodies emerged rapidly, the seropositive rate of binding antibodies and seroconversion rate of neutralizing antibodies was 99% and 50%, respectively. From 3 to 12 months, the binding and neutralizing antibodies declined slightly overtime. At 12 months, the binding and neutralizing antibodies were still detectable and significantly higher than the baseline. IFN-γ and IL-2 secretion specifically induced by RBD persisted at high levels until 6 months, and could be observed at 12 months, while the levels of IL-5 and Granzyme B were hardly detected, demonstrating a Th1-biased response. Besides, specific CD4+TCM, CD4+TEMM, CD8+ TEMand CD8+TE cells were all detectable and functional up to 12 months after the second dose, as the cells produced IFN-γ, IL-2, and GzmB in response to stimulation of SARS-CoV-2 RBD. Interpretation: CoronaVac not only induced durable binding and neutralising antibody responses, but also SARS-CoV-2-specific CD4+ and CD8+ memory T cells for up to 12 months. Trial Registration: This study is registered with ClinicalTrials.gov, NCT05072496. Funding: Beijing Municipal Science & Technology Commission Declaration of Interest: None to declare. Ethical Approval: The trial protocol was approved by the Ethics Committee of Beijing CDC (2020-28)