To gain insight into the different protective mechanisms of approved vaccines, this
study focuses on the comparison of humoral and cellular immune responses of five widely
used vaccines including ChAdOx1 (AZD1222, AstraZeneca), BNT162b2 (Pfizer), mRNA-1273
(Moderna), BBIBP-CorV (Sinopharm), and Gam-COVID-Vac (Sputnik V).Isolated plasma from
95 volunteers' blood samples was used to measure anti-SARS-CoV-2 humoral and cellular
immune responses. Positive controls were recovered patients from COVID-19 (unvaccinated).
Specific quantification kits for anti-nucleocapsid IgG, anti-Spike protein IgG, neutralizing
antibodies as well as specific SARS-CoV-2 antigens for T-cell activation were used
and Spearman correlation and matrix analyses were performed to compare overall immune
responses.Nucleocapsid antibodies were significantly higher for the BBIBP-CorV and
convalescent group when compared to other vaccines. In contrast, subjects vaccinated
with BNT162b2 and mRNA-1273 presented significantly higher anti-spike IgG. In fact,
9.1% of convalescent, 4.5% of Gam-COVID-Vac, 28.6% of ChAdOx1, and 12.5% of BBIBP-CorV
volunteers did not generate anti-spike IgG. Similarly, a positive correlation was
observed after the neutralization assay. T-cell activation studies showed that mRNA-based
vaccines induced a T-cell driven immune response in all cases, while 55% of convalescents,
8% of BNT162b1, 12,5% of mRNA-1273, 9% of Gam-COVID-Vac, 57% of ChAdOx1, and 56%
of BBIBP-CorV subjects presented no cellular response. Further correlation matrix
analyses indicated that anti-spike IgG and neutralizing antibodies production, and
T-cell activation follow the same trend after immunization.RNA-based vaccines induced
the most robust adaptive immune activation against SARS-CoV-2 by promoting a significantly
higher T-cell response, anti-spike IgG and neutralization levels. Vector-based vaccines
protected against the virus at a comparable level to convalescent patients.
