Increased Antibody Titers but Induced T-Cell AICD and Apoptosis Response in COVID-19 Convalescents by Inactivated Vaccine Booster

It is urgently needed to evaluate the necessity and benefits of booster vaccination to facilitate clinical decision-making for recovered COVID-19 patients. In this study, we conducted a multicentre, prospective clinical trial of the earliest COVID-19 patients with a definitive history of direct or indirect exposure to SARS-CoV-2 through Hubei Province from three Chinese hospitals to evaluate the efficiency, safety and immune response of CoronaVac (an inactivated COVID-19 vaccine). Convalescent patients with high titres (≥ 1:96) or non-severe also exhibited higher frequency of long COVID-19 symptoms. One booster dose in convalescent patients with antibody titres below 1:96 significantly induced neutralizing antibodies against prototypic SARS-CoV-2 and the Delta variant by 13.03- and 9.27-fold, respectively. Transient adverse events occurred in three out of the twenty-eight immunized participants (10.71%). In addition, the ratio of naïve T cells increased dramatically, and TEMRA and TEM cells gradually decreased post vaccination. The expression levels of activation-induced cell death and apoptosis-related genes were significantly elevated after vaccination in all T-cell subtypes in convalescent patients. Our results indicate that vaccine-mediated T-cell consumption and regeneration patterns may be detrimental to the antiviral response. We generated a single-cell combined transcriptome (single-cell RNA-seq [scRNA- seq], T-cell receptor [TCR] and B-cell receptor [BCR]) for three convalescent patients who experienced the most apparent increases in naïve T cells before (day 0) and after vaccination (day 28) using 10× Genomics platform.