Anti-SARS-CoV-2 Receptor-Binding Domain Total Antibodies Response in Seropositive and Seronegative Healthcare Workers Undergoing COVID-19 mRNA BNT162b2 Vaccination

Abstract

Background: This study monitored total anti-SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) RBD (receptor-binding domain) antibodies levels in a large population of healthcare workers undergoing mRNA COVID-19 vaccination. Methods. The study population consisted of employees of Pederzoli Hospital of Peschiera del Garda (Verona, Italy), who underwent voluntary vaccination with two doses of COVID-19 mRNA BNT162b2 (Comirnaty; Pfizer Inc). Venous blood was drawn immediately before the first vaccine dose, as well as 21 days (immediately before second vaccine dose) and 50 days afterwards. Humoral response was assessed with Roche Elecsys Anti-SARS-CoV-2 S total antibodies, on Roche Cobas 6000 (Roche Diagnostics). Results: The final study population consisted of 925 subjects (mean age, 44 ± 13 years; 457 women), 206 (22.3%) anti-SARS-CoV-2 baseline seropositive. The increase of total anti-SARS-CoV-2 RBD antibodies levels 21 days after the first vaccine dose was ~3 orders of magnitude higher in seropositive than in seronegative individuals (11782 vs. 42 U/mL; p < 0.001). Total anti-SARS-CoV-2 RBD antibodies levels further increased by over 30-fold after the second vaccine dose in baseline seronegative subjects, while such increase was only ~1.3-fold in baseline seropositive subjects. In multivariate analysis, total anti-SARS-CoV-2 RBD antibodies level was inversely associated with age after both vaccine doses and male sex after the second vaccine dose in baseline seronegative subjects, while baseline antibodies value significantly predicted immune response after both vaccine doses in baseline seropositive recipients. Conclusion: Significant difference exists in post-mRNA COVID-19 vaccine immune response in baseline seronegative and seropositive subjects, which seems dependent on age and sex in seronegative subjects, as well as on baseline anti-SARS-CoV-2 antibodies level in seropositive patients.

BNT162b2 mRNA SARS-CoV-2 Vaccine Elicits High Avidity and Neutralizing Antibodies in Healthcare Workers

“…The amounts of IgG and IgA anti-RBD antibodies far exceed those observed in COVID-19 patients, suggesting a highly efficient antigen production and presentation in all the subjects [ 18 ]…”

Anti-SARS-CoV-2 Antibodies Testing in Recipients of COVID-19 Vaccination: Why, When, and How?

“…For example, the two-dose complete cycle of mRNA COVID-19 vaccination seems to generate a lower relative increase of anti-SARS-CoV-2-neutralizing antibodies in people with a previous SARS-CoV-2 infection than in those who were not infected by the virus. This seems mostly attributable to the fact that most people with a previous SARS-CoV-2 infection have already developed a straightforward humoral, cellular, and memory immune response, and thus a further increase of anti-SARS-CoV-2 antibodies after the second vaccine dose is modest in subjects who have strongly responded to the first [10][11][12][13]. Notably, a significant correlation has been observed between pre-vaccination anti-SARS-CoV-2 antibodies titer and Pfizer BNT162b2 vaccine immunogenicity, whereby the anti-SARS-CoV-2 RBD (receptor binding domain) total antibodies response seems to be reduced (up to nearly eightfold) in patients with a baseline antibody level in the upper quartile [11].…”

“…This seems mostly attributable to the fact that most people with a previous SARS-CoV-2 infection have already developed a straightforward humoral, cellular, and memory immune response, and thus a further increase of anti-SARS-CoV-2 antibodies after the second vaccine dose is modest in subjects who have strongly responded to the first [10][11][12][13]. Notably, a significant correlation has been observed between pre-vaccination anti-SARS-CoV-2 antibodies titer and Pfizer BNT162b2 vaccine immunogenicity, whereby the anti-SARS-CoV-2 RBD (receptor binding domain) total antibodies response seems to be reduced (up to nearly eightfold) in patients with a baseline antibody level in the upper quartile [11]. Therefore, with 50% (or even more) of all SARS-CoV-2 infections remaining completely asymptomatic up to negativization of molecular testing [14,15], the organization of pre-vaccination serological surveys represents a reliable mean for unmasking all SARS-CoV-2 seropositive subjects in whom vaccine administration may be personalized, adapted, or even delayed based on their actual anti-SARS-CoV-2 antibodies status [16].…”

Importance of sample dilution in the evaluation of the antibody response after SARS-CoV-2 vaccination

“…In conclusion, we agree with Tré-Hardy et al that a persistent antibody response was observe following the administration of the mRNA vaccine, as observed elsewhere using various assays. ( 1 , 2 , 3 , 4 , 7 ) However, the absence of “antibody drop” between T1, T2 and T3 observed in their cohort of previously seropositive could depend on the analytical kit used and the application of a dilution factor in case of signal saturation if such procedure is permitted and documented by the manufacturer. The results of the CRO-VAX HCP study showed that the use of undiluted or diluted samples led to different conclusions regarding the antibody kinetics.…”

“…( 4 , 5 ) Nevertheless, in previous investigations, sample dilutions were applied to allow a better discrimination between previously seronegative and seropositive subjects. ( 6 , 7 , 8 , 9 ) Compared to the antibody response observed in past-COVID-19 patients, where none or few samples needed to be diluted,( 2 , 9 , 10 ) the antibody response in vaccinees is significantly higher and will certainly require dilutions to obtain the real quantitative value with some assays (i.e. not rounded to the upper limit of measurement).…”