Introduction: Similar to antibody detection, severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2)-specific T-cell response evaluation is also pivotal among the coronavirus disease 2019 (COVID-19) convalescents and the vaccinated populations. Nucleocapsid (N) protein is one of the main structural proteins of SARS-CoV-2 and can trigger T-cell responses in humans.Methods: An overlapping peptide pool covering the full length of the N protein was designed, peptides with positive T-cell activating potency in COVID-19 convalescents were screened, and CD8 + T cell epitopes were further identified. The epitope was used to detect the SARS-CoV-2-specific CD8 + T cell responses in COVID-19 convalescents based in intracellular cytokine staining and tetramer staining in flow cytometry.Results: A human leukocyte antigen A (HLA-A)*1101-restricted CD8 + T cell epitope, which could stimulate the production of IFN-γ via peripheral blood mononuclear cells (PBMCs) of the convalescents was defined, and the tetramer generated with this epitope could detect SARS-CoV-2-specific T cells in the PBMCs of the convalescents. The structural investigation eliminated that the epitope was a typical HLA-A*1101-restricted T-cell epitope which was conserved among all the sarbecoviruses.Discussion: The newly identified SARS-CoV-2derived T-cell epitope was helpful to detect the cellular immunity against different sarbecoviruses including SARS-CoV and SARS-CoV-2. This study provided an evaluation method and also a peptide candidate for the research and development of T-cell based vaccine for the virus.

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Background Recent seasonal epidemics of influenza have been caused by human influenza A viruses of the H1N1 and H3N2 subtypes and influenza B viruses. Annual vaccination is recommended to prevent infection; however, how annual influenza vaccination influences vaccine effectiveness is largely unknown. Methods To investigate the impact of repeated vaccination on immune and protective effect, we performed a prospective seroepidemiologic study. Participants with or without prior vaccination (2018–2019) were enrolled during the 2019–2020 influenza season. Inactivated quadrivalent influenza vaccine (IIV4) was administered through the intramuscular route, and venous blood samples were collected regularly to test hemagglutination inhibition (HAI) titers. Results The geometric mean titers and proportion with titers ≥40 against the influenza vaccine components peaked at 30 days post‐vaccination. At Day 30, the geometric mean titer and proportion with titers ≥40 in participants who had been previously vaccinated were higher for H3N2 but similar for both B lineages (Victoria and Yamagata) as compared with participants vaccinated for the first time. As for H1N1, the geometric mean titer was lower in repeated vaccinated participants, but the proportion with titers ≥40 was consistent in both groups. Conclusions Repeated vaccination provides similar or enhanced protection as compared with single vaccination in first‐time vaccinees.

For nearly three years, humans have experienced multiple rounds of global transmission of SARS-CoV-2 and its variant strains. In addition, the widely used vaccines against SARS-CoV-2 involve multiple strategies of development and inoculation, globally. Thus, the acquired immunity established among humans is quite complicated, and there is still a lack of understanding within a panoramic vision. Here, we provide the special characteristics of the cellular and humoral immune responses in 2-year convalescents after the inoculation of inactivated vaccine, in parallel to vaccinated COVID-19 naïve persons and unvaccinated controls. The decreasing trends of the IgG, IgA, and neutralizing antibodies (NAb), but not IgM of the convalescents were reversed by the vaccination. Both cellular and humoral immunity to SARS-CoV-2 in convalescents after vaccination were higher than the vaccinated COVID-19 naïve persons. Notably, the inoculation of inactivated vaccine fueled the NAb to Omicron BA.1, BA.2, BA.4, and BA.5 in the 2-year convalescents, much higher than the NAb during 6 months and 1 year after symptoms onset. And no obvious T cell escaping to the S protein was observed after the inoculation in the 2-year convalescents. The study provides insight into the complicated features of acquired immunity of humans to SARS-CoV-2 and variants in the real world, and indicated that promoting vaccine inoculation is an essential way to achieve herd immunity against emerging viral variants for the ongoing COVID-19 pandemic, including the convalescents.

Over three years, humans have experienced multiple rounds of global transmission of SARS-CoV-2 and its variants. In addition, the widely used vaccines against SARS-CoV-2 involve multiple strategies of development and inoculation. Thus, the acquired immunity established among humans is complicated, and there is a lack of understanding within a panoramic vision. Here, we provide the special characteristics of the cellular and humoral responses in 2-year convalescents after inactivated vaccines, in parallel to vaccinated COVID-19 naïve persons and unvaccinated controls. The decreasing trends of the IgG, IgA, and NAb, but not IgM of the convalescents were reversed by the vaccination. Both cellular and humoral immunity in convalescents after vaccination were higher than the vaccinated COVID-19 naïve persons. Notably, inoculation with inactivated vaccine fueled the NAb to BA.1, BA.2, BA.4, and BA.5 in 2-year convalescents, much higher than the NAb during 6 months and 1 year after symptoms onset. And no obvious T cell escaping to the S protein was observed in 2-year convalescents after inoculation. The study provides insight into the complicated features of human acquired immunity to SARS-CoV-2 and variants in the real world, indicating that promoting vaccine inoculation is essential for achieving herd immunity against emerging variants, especially in convalescents.