Phoksawat W.Nithichanon A.Lerdsamran H.Wongratanacheewin S.Meesing A.Pipattanaboon C.Kanthawong S.Aromseree S.Yordpratum U.Laohaviroj M.Lulitanond V.Chareonsudjai S.Puthavathana P.Kamuthachad L.Kamsom C.Thapphan C.Salao K.Chonlapan A.Nawawishkarun P.Prasertsopon J.Overgaard H.J.Edwards S.W.Phanthanawiboon S.Mahidol University2023-06-182023-06-182022-11-15Vaccine Vol.40 No.48 (2022) , 6963-69700264410Xhttps://repository.li.mahidol.ac.th/handle/20.500.14594/83556Background: 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 hospitalization, but less is known whether it elicits long-term T cell responses and provides prolonged protection. 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 cytometry. 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.Biochemistry, Genetics and Molecular BiologyArticleSCOPUS10.1016/j.vaccine.2022.10.0172-s2.0-851407810681873251836283898