Population-Based Analysis of the Immunoglobulin G Response to Different COVID-19 Vaccines in Brazil

Abstract

(1) Background: COVID-19 vaccination in Brazil has been performed mostly with CoronaVac (Sinovac), ChAdOx1-S (AstraZeneca-University of Oxford) and BNT162b2 (Pfizer-BioNTech) vaccines. The titers of IgG antibodies reactive to the SARS-CoV-2 spike protein correlate with vaccine efficacy. Studies comparing vaccine immunogenicity in a real-world scenario are lacking. (2) Methods: We performed a population-based study to analyze the immunoglobulin G response to different COVID-19 vaccines. Citizens older than 18 years (n = 2376) provided personal data, a self-declaration of any previous COVID-19 positive tests and information regarding COVID-19 vaccination: the vaccine popular name and the date of each dose. Blood samples were collected and the levels of IgG reactive to SARS-CoV-2 antigens were determined and compared between different vaccine groups. (3) Results: The seroconversion for anti-spike IgG achieved > 95% by February 2022 and maintained stable until June 2022. Higher anti-spike IgG titers were detected in individuals vaccinated with BNT162b2, followed by ChAdOx1-S and CoronaVac. The anti-spike IgG response was negatively correlated with age and interval after the second dose for the BNT162b2 vaccine. Natural infections boosted anti-spike IgG in those individuals who completed primary vaccination with ChAdOx1-S and CoronaVac, but not with BNT162b2. The levels of anti-spike IgG increased with the number of vaccine doses administered. The application of BNT162b2 as a 3rd booster dose resulted in high anti-spike IgG antibody titers, despite the type of vaccine used during primary vaccination. (4) Conclusions: Our data confirmed the effectiveness of the Brazilian vaccination program. Of the vaccines used in Brazil, BNT162b2 performed better to elicit anti-spike protein IgG after primary vaccination and as a booster dose and thus should be recommended as a booster whenever available. A continuous COVID-19 vaccination program will be required to sustain anti-spike IgG antibodies in the population.

Keywords: SARS-CoV-2; humoral response; vaccine.

Figure 1

The IgG response to spike protein and S1 RBD accordingly to the vaccine type. IgG levels reactive to spike protein (A) and S1 RBD (B) in participants negative for COVID-19 who completed primary vaccination (2nd dose) between 10 and 240 days. Bars represent the geometric mean with 95% CI, the dashed line indicates the seropositive cutoff. Pre-pandemic samples were plotted as controls. One-way ANOVA analysis was performed, all comparisons were significant at p < 0.0001 except when indicated in the graph (* p < 0.05), (ns, not significant). Numbers above the graph indicate seroconversion rates. The dashed line indicates the seropositive assay cutoff.

Figure 2

Correlation between the levels of IgG reactive to spike and the age or time after the second vaccine dose. The IgG levels were determined in participants negative for COVID-19 who completed primary vaccination (2nd dose) between 10 and 240 days. (A) Correlations between IgG levels and age. (B) Correlations between IgG levels and time after the second dose. (C) Correlations between age and time after the second dose. The linear regression with 95% CI and Pearson’s correlation coefficient is indicated. Color code, green BNT162b2, red ChAdOx1-S, blue CoronaVac.

Figure 3

The levels of IgG reactive to spike protein in response to infection and vaccination. (A) Participants that completed the primary vaccination (2nd dose) were grouped accordingly to the vaccine type. Those participants who self-declared a previous positive COVID-19 test are indicated as infection cases. (B) Participants were grouped accordingly to the number of vaccine doses. The dashed line indicates the seropositive assay cutoff. Pre-pandemic samples were plotted as naïve controls. Bars represent the geometric mean and 95% CI. One-way ANOVA analysis was performed, and comparisons were all significant (p < 0.02) unless indicated as not significant (ns).

Figure 4

IgG levels reactive spike after completion of primary vaccination and after the booster dose accordingly to the vaccine type. IgG levels reactive for spike in all participants (including those negative and positive for natural infections) who completed primary vaccination (2nd dose) between 10 and 240 days are indicated accordingly to the vaccine type. The IgG levels in participants who took a 3rd booster dose is indicated with + followed by the vaccine type of the booster. Only participants who took the booster dose between 10 and 240 days were considered. The dashed line indicates the seropositive assay cutoff. The geometric mean and 95% CI are represented by the bars. Number indicates the seroconversion rates.