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. 2022 Nov 21;17(11):e0277827.
doi: 10.1371/journal.pone.0277827. eCollection 2022.

Combined monitoring of IgG and IgA anti-Spike and anti-Receptor binding domain long term responses following BNT162b2 mRNA vaccination in Greek healthcare workers

Ioannis Sarrigeorgiou  1 , Dimitra Moschandreou  2 , Alexios Dimitriadis  3 , Gerasimina Tsinti  1 , Evangelia Sotiropoulou  3 , Eleni Ntoukaki  1 , Petros Eliadis  3   4 , Marija Backovic  5 , Stavroula Labropoulou  6 , Nicolas Escriou  7 , Abraham Pouliakis  8 , Georgia Giannopoulou  2 , Eleni Gaitanarou  2 , Konstantinos Lazaridis  1 , Andreas Mentis  6 , Avgi Mamalaki  3   4 , Elisavet Grouzi  2 , Peggy Lymberi  1
Affiliations

Combined monitoring of IgG and IgA anti-Spike and anti-Receptor binding domain long term responses following BNT162b2 mRNA vaccination in Greek healthcare workers

Ioannis Sarrigeorgiou et al. PLoS One. .

Abstract

Studies on the humoral response to homologous BNT162b2 mRNA-vaccination focus mainly on IgG antibody dynamics, while long-term IgA kinetics are understudied. Herein, kinetics of IgG and IgA levels against trimeric-Spike (S) and Receptor-Binding-Domain (RBD) were evaluated by in-house ELISAs in 146 two-dose vaccinated Greek healthcare workers (HCWs) in a 9-month period at six time points (up to 270 days after the first dose). The effect of a homologous booster third dose was also studied and evaluated. The peak of immune response was observed 21 days after the second dose; 100% seroconversion rate for anti-S and anti-RBD IgG, and 99.7% and 96.3% respectively for IgA. IgG antibody levels displayed higher increase compared to IgA. Declining but persistent anti-SARS-CoV-2 antibody levels were detected 9 months after vaccination; IgG and IgA anti-S levels approached those after the first dose, while a more rapid reduction rate for anti-RBD antibodies led to significantly lower levels for both classes, supporting the need for a booster dose. Indeed, a homologous booster third dose resulted in enhanced levels of anti-S of both classes, whereas anti-RBD didn't exceed the peak levels after the second dose. Previous SARS-CoV-2 infection, flu vaccination, BMI<35 and the occurrence of an adverse event upon vaccination, were associated with higher IgG antibody levels over time, which however were negatively affected by age increase and the presence of chronic diseases. Overall, after concurrently using the S and RBD target-antigens in in-house ELISAs, we report in addition to IgG, long-term persistence of IgA antibodies. Regarding antibody levels, homologous mRNA vaccination gives rise to an effective anti-viral protection up to 9 months negatively correlated to age. Considering that COVID-19 is still a matter of public concern, booster vaccine doses remain critical to vulnerable individuals.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. In-house ELISA validation.
The sensitivity and specificity of the in-house ELISAs for IgG (A) and for IgA (B) Abs against S and RBD were estimated with 40 pre-pandemic sera (Healthy C.) and 40 PCR+ COVID-19 sera. For IgG anti-S and anti-RBD Abs the cut-off point was 150 AU/well (dashed line). For IgA Abs the cut-off point for anti-S was 120 AU/well and for anti-RBD 80 AU/well (dashed lines).
Fig 2
Fig 2. Serum anti-N IgG and IgA antibody levels prior to vaccination.
For PCR- Naïve individuals (n = 134) and PCR+ (n = 12) individuals the sample prior to vaccination was on Day0. The cut-off point of IgG and IgA ELISAs was established at 400 AU/well and 170 AU/well, respectively (dashed lines). Asterisks (*) indicate statistically significant differences (p-value: **<0.01, ***<0.001) between the compared groups. Each dot represents an individual and error bars represent the mean value and standard deviation of the distribution.
Fig 3
Fig 3. IgG anti-S and anti-RBD levels post-vaccination.
Anti-S (blue) and anti-RBD (red) Abs were measured on Day 0, 21, 42, 90, 180 and 270 days after the first dose on Day0. Cut-off values for anti-S and anti-RBD Abs were 150 AU/well (dashed line). Dark colored dots represent post-vaccination infected individual’s anti-S and anti-RBD IgG levels respectively. Asterisks (***) indicate statistically significant differences (p-value<0.001) between the compared groups. Each dot represents an individual, and error bars represent the mean value and standard deviation of the distribution.
Fig 4
Fig 4. IgA anti-S and anti-RBD levels post-vaccination.
Anti-S (blue) and anti-RBD (red) Abs were measured on Day0, 21, 42, 90, 180 and 270 (n = 56). Cut-off values for anti-S and anti-RBD Abs were 120 AU/well and 80 AU/well, respectively (dashed lines). Asterisks (***) indicate statistically significant differences (p-value < 0.001) between the compared groups. Each dot represents an individual, and error bars represent the mean value and standard deviation of the distribution.
Fig 5
Fig 5. IgG and IgA rate of change up to 9-months post-vaccination.
IgG (A) and IgA (B) RC values express the average change per day and were estimated for two subsequent time points: Day0-Day21 = RC0–1, Day21-Day42 = RC1–2, Day42-Day90 = RC2–3, Day90-Day180 = RC3–6, Day180-Day270 = RC6–9. Positive values indicate an increase in production, negative values imply a decrease, and values close to zero show no change in anti-S (blue) and anti-RBD (red) antibody binding. Asterisks (*) indicate statistically significant differences (p-value: *<0.05, ***<0.001). Each dot represents an individual, and error bars represent the mean value and standard deviation of the distribution.
Fig 6
Fig 6. IgG anti-S and anti-RBD kinetics in a 9-month period: PCR+ individuals (red, n = 12 COVID-19), naïve individuals (green, n = 131) and suspected COVID-19 asymptomatic individuals (blue, n = 3).
IgG anti-S (A) and anti-RBD (B) Abs were measured on Day0, 21, 42, 90, 180 and 270 days after the first dose. For each group, mean and standard deviation values are given for every time-point. Asterisks (*) indicate statistically significant differences (p-value: *<0.05, **<0.001, ***0.001) between the groups of PCR+ and naïve individuals.
Fig 7
Fig 7. Antibody levels for 34 HCWs who received a third dose of the BNT162b2 mRNA vaccine.
IgG (A) and IgA (B) anti-S (blue) and anti-RBD (red) Abs were measured on Day0, 42, 90, 270 days after the first dose on Day0 and on Day21γ, 21 days after the third dose. Asterisks (***) indicate statistically significant differences (p-value: <0.001). Each dot represents an individual and error bars represent the mean value and standard deviation of the distribution.
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Grants and funding

We acknowledge support of this work by the HPI (Decision of the Administration Council, Reference Number: 14365 / 28.12.2020) and the project ‘INSPIRED’ (MIS 5002550), under the Action ‘Reinforcement of the Research and Innovation Infrastructure’, funded by the Operational Program ‘Competitiveness, Entrepreneurship and Innovation’ (NSRF 2014‐2020); action co-funded by the Greek Government and the European Union—European Regional Development Fund. https://www.pasteur.grhttps://www.pasteur.gr/espa/ The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.