Salivary, serological, and cellular immune response to the CoronaVac vaccine in health care workers with or without previous COVID-19.

We investigated the anti-SARS-CoV-2 post-vaccine response through serum and salivary antibodies, serum antibody neutralizing activity and cellular immune response in samples from health care workers who were immunized with two doses of an inactivated virus-based vaccine (CoronaVac) who had or did not have COVID-19 previously. IgA and IgG antibodies directed at the spike protein were analysed in samples of saliva and/or serum by ELISA and/or chemiluminescence assays; the neutralizing activity of serum antibodies against reference strain B, Gamma and Delta SARS-CoV-2 variants were evaluated using a virus neutralization test and SARS-CoV-2 reactive interferon-gamma T-cell were analysed by flow cytometry. CoronaVac was able to induce serum and salivary IgG anti-spike antibodies and IFN-γ producing T cells in most individuals who had recovered from COVID-19 and/or were vaccinated. Virus neutralizing activity was observed against the ancestral strain, with a reduced response against the variants. Vaccinated individuals who had previous COVID-19 presented higher responses than vaccinated individuals for all variables analysed. Our study provides evidence that the CoronaVac vaccine was able to induce the production of specific serum and saliva antibodies, serum virus neutralizing activity and cellular immune response, which were increased in previously COVID-19-infected individuals compared to uninfected individuals.

SARS-CoV-2 recombinant proteins stimulate distinct cellular and humoral immune response profiles in samples from COVID-19 convalescent patients.

OBJECTIVES: In this preliminary study we investigated cellular and humoral immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in blood samples from 14 recovered coronavirus disease 2019 (COVID-19) patients and compared them to those in samples from 12 uninfected/unvaccinated volunteers. METHODS: Cellular immunity was assessed by intracellular detection of IFN-γ in CD3+ T lymphocytes after stimulation with SARS-CoV-2 spike (S1), nucleocapsid (NC), or receptor-binding domain (RBD) recombinant proteins or overlapping peptide pools covering the sequence of SARS-CoV-2 spike, membrane and nucleocapsid regions. The humoral response was examined by ELISAs and/or chemiluminescence assays for the presence of serum IgG antibodies directed to SARS-CoV-2 proteins. RESULTS: We observed differences between humoral and cellular immune profiles in response to stimulation with the same proteins. Assays of IgG antibodies directed to SARS-CoV-2 NC, RBD and S1/S2 recombinant proteins were able to differentiate convalescent from uninfected/unvaccinated groups. Cellular immune responses to SARS-CoV-2 protein stimuli did not exhibit a specific response, as T cells from both individuals with no history of contact with SARS-CoV-2 and from recovered donors were able to produce IFN-γ. CONCLUSIONS: Determination of the cellular immune response to stimulation with a pool of SARS-CoV-2 peptides but not with SARS-CoV-2 proteins is able to distinguish convalescent individuals from unexposed individuals. Regarding the humoral immune response, the screening for serum IgG antibodies directed to SARS-CoV-2 proteins has been shown to be specific for the response of recovered individuals.

Prevalence of anti-SARS-CoV-2 antibodies in outpatients of a large public university hospital in Sao Paulo, Brazil.

Coronavirus disease 19 (COVID-19) is caused by SARS-Cov-2 and the manifestations of this infection range from an absence of symptoms all the way up to severe disease leading to death. To estimate the prevalence of past infection in a population, the most readily available method is the detection of antibodies against the virus. This study has investigated the prevalence of anti-SARS-CoV-2 antibodies in outpatients of the Hospital das Clinicas, in Sao Paulo city (Brazil), which is a large university hospital belonging to the public health system that cares for patients with complex diseases who need tertiary or quaternary medical care. Our serological inquiry was carried out for 6 weeks, with once-a-week blood sampling and included 439 patients from several outpatient services. Overall, 61 patients tested positive for anti-SARS-CoV-2 IgG (13.9%); 56.1 % of the patients live in Sao Paulo city, with the remaining living in other towns of the metropolitan area; 32.8% of the patients testing positive for IgG antibodies to SARS-CoV-2 were asymptomatic, 55.7% developed mild or moderate disease and 11.5% had to be hospitalized. The prevalence of SARS-CoV-2 positive serology was lower among patients who had received the seasonal influenza vaccine compared to the ones who did not. These findings may indicate that those individuals care more about health issues, and/or that they have a better access to health care and/or a better quality of health care service. The large proportion of patients who were unaware of having had contact with SARS-CoV-2 deserves attention, reflecting the scarcity of tests performed in the population.