Anti-Spike SARS-CoV-2 IgG Assessment with a Commercial Assay during a 4-Month Course after COVID-19 Vaccination

Abstract

We intended to assess the humoral response induced by the Pfizer/BioNTech Comirnaty COVID-19 vaccine with commercially available immunoassays: anti-spike (S) IgG and IgM, and anti-nucleocapsid (N) IgG antibodies, over a 4-month course. One hundred subjects, including 15 COVID-19 convalescents, comprised the study cohort. The SARS-CoV-2 antibodies concentrations were measured on day 0' and 10', 20', 30', 60', 90', and 120' after the first dose administration. Over the course of the study, 100% of the participants developed and sustained anti-SARS-CoV-2 S IgG antibodies. The highest concentration, exceeding the quantification range of the test (2080 BAU/mL), was reached by 67% of the subjects on day 30'. The concentration of the antibodies remained stable between days 30' and 90' but was followed by a significant decrease between days 90' and 120'. The stronger and more persistent humoral response was noted for women. The COVID-19 convalescents developed higher antibody levels, particularly 10 days after the first Comirnaty dose. Twenty-three out of the eighty-five naïve vaccinees failed to develop a detectable IgM response. LIAISON^® SARS-CoV-2 TrimericS IgG (DiaSorin S.p.A, Saluggia, Italy) may be useful in the assessment of the humoral response to the Comirnaty vaccine. In contrast, Abbott's anti-S SARS-CoV-2 IgM has a limited utility in this context.

Keywords: COVID-19 testing; COVID-19 vaccines; COVID-19 vaccines booster shot; SARS-CoV-2 antibodies.

Figure 1

The percentage of the patients reaching given antibody levels at the consecutive time points after vaccination. Results obtained with LIAISON^® SARS-CoV-2 TrimericS IgG assay; >33.8 BAU/mL—cut-off for the positive result; >520 BAU/mL—antibody concentration correlated with a high neutralization capability; >2080 BAU/mL—upper limit of the assay’s quantification range.

Figure 2

The serodynamics of the anti-spike IgG production after vaccination in the whole cohort. The results obtained with LIAISON^® SARS-CoV-2 TrimericS IgG assay at each of the time points are shown as median (q25, q75). The significant differences between the measurements (p < 0.05) at the consecutive time points are indicated with *.

Figure 3

The comparison of the serodynamics of the anti-spike IgG production in the subgroup of COVID-19 convalescents (blue) and naïve vaccinees (orange). The results were obtained with LIAISON^® SARS-CoV-2 TrimericS IgG and are shown as median (q25, q75). The significant differences (p < 0.05) between the measurements at the consecutive time points are indicated with *.

Figure 4

The comparison of the serodynamics of the anti-spike IgG production in the subgroups of non-convalescent females (blue) and males (orange). The results were obtained with LIAISON^® SARS-CoV-2 TrimericS IgG assay and are shown as median (q25, q75). The significant differences (p < 0.05) between the measurements at the consecutive time points are indicated with *.

Figure 5

The comparison of the serodynamics of the anti-spike IgG production in the subgroup of non-convalescent subjects below 60 y/o (blue) and over 60 y/o (orange). The results were obtained with LIAISON^® SARS-CoV-2 TrimericS IgG assay and are shown as median (q25, q75). The significant differences (p < 0.05) between the measurements at the consecutive time points are indicated with *.

Figure 6

The scatter plot showing association between age and antibody level 120 days after vaccination in non-COVID-19-convalescents. The results obtained with LIAISON^® SARS-CoV-2 TrimericS IgG assay. No correlation was found (r = −0.045).

Figure 7

The percentage of the patients reaching a cut-off for a positive result of anti-S IgM antibodies at the consecutive time points after vaccination. Results obtained with SARS-CoV-2 S IgM Abbott assay.