Phenotypic and functional changes of T cell subsets after CoronaVac vaccination

Background: The pandemic coronavirus disease 2019 (COVID-19) is a major global public health concern and several protective vaccines, or preventive/therapeutic approaches have been developed. Sinovac-CoronaVac, an inactivated whole virus vaccine, can protect against severe COVID-19 disease and hospi-talization, but less is known whether it elicits long-term T cell responses and provides prolonged protec-tion.Methods: This is a longitudinal surveillance study of SARS-CoV-2 receptor binding domain (RBD)-specific IgG levels, neutralizing antibody levels (NAb), T cell subsets and activation, and memory B cells of 335 participants who received two doses of CoronaVac. SARS-CoV-2 RBD-specific IgG levels were measured by enzyme-linked immunosorbent assay (ELISA), while NAb were measured against two strains of SARS-CoV-2, the Wuhan and Delta variants. Activated T cells and subsets were identified by flow cytom-etry. Memory B and T cells were evaluated by enzyme-linked immune absorbent spot (ELISpot). Findings: Two doses of CoronaVac elicited serum anti-RBD antibody response, elevated B cells with NAb capacity and CD4' T cell-, but not CD8' T cell-responses. Among the CD4' T cells, CoronaVac activated mainly Th2 (CD4' T) cells. Serum antibody levels significantly declined three months after the second dose.Interpretation: CoronaVac mainly activated B cells but T cells, especially Th1 cells, were poorly activated. Activated T cells were mainly Th2 biased, demonstrating development of effector B cells but not long-lasting memory plasma cells. Taken together, these results suggest that protection with CoronaVac is short-lived and that a third booster dose of vaccine may improve protection.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The study showed that CoronaVac mainly activated antibody and certain T cell responses in the short term, but lacked long-lasting memory T cell responses, providing only short-lived protection, suggesting that a third booster dose of vaccine may improve protection.