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-gamma 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.

Automated summary

We investigated the immune response to the SARS-CoV-2 vaccine (CoronaVac) in healthcare workers who had received two doses of the inactivated virus-based vaccine. Our study analyzed serum and salivary antibodies, serum antibody neutralizing activity, and cellular immune response. The results showed that CoronaVac induced the production of specific serum and saliva antibodies, as well as IFN-gamma producing T cells, in most individuals who had recovered from COVID-19 and/or were vaccinated. The vaccine demonstrated neutralizing activity against the ancestral strain, but a reduced response against the variants. Vaccinated individuals with previous COVID-19 infection exhibited higher immune responses compared to those without previous infection.