Boosting of the SARS-CoV-2-Specific Immune Response after Vaccination with Single-Dose Sputnik Light Vaccine

Abstract

Despite measures taken world-wide, the coronavirus disease 2019 (COVID-19) pandemic continues. Because efficient antiviral drugs are not yet widely available, vaccination is the best option to control the infection rate. Although this option is obvious in the case of COVID-19-naive individuals, it is still unclear when individuals who have recovered from a previous SARS-CoV-2 infection should be vaccinated and whether the vaccination raises immune responses against the coronavirus and its novel variants. In this study, we collected peripheral blood from 84 healthy human donors of different COVID-19 status who were vaccinated with the Sputnik Light vaccine and measured the dynamics of the Ab and T cell responses, as well as the virus-neutralizing activity (VNA) in serum, against two SARS-CoV-2 variants, B.1.1.1 and B.1.617.2. We showed that vaccination of individuals previously exposed to the virus considerably boosts the existing immune response. In these individuals, receptor-binding domain (RBD)-specific IgG titers and VNA in serum were already elevated on the 7th day after vaccination, whereas COVID-19-naive individuals developed the Ab response and VNA mainly 21 d postvaccination. Additionally, we found a strong correlation between RBD-specific IgG titers and VNA in serum, and according to these data vaccination may be recommended when the RBD-specific IgG titers drop to 142.7 binding Ab units/ml or below. In summary, the results of the study demonstrate that vaccination is beneficial for both COVID-19-naive and recovered individuals, especially since it raises serum VNA against the B.1.617.2 variant, one of the five SARS-CoV-2 variants of concern.

Conflict of interest statement

The authors have no financial conflicts of interest.

Copyright © 2022 by The American Association of Immunologists, Inc.

Figures

FIGURE 1.

Dynamics of the Ab and T cell responses. (A and B) Titers of the IgGs specific to the receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) protein (A) and frequencies of the S protein–specific T cells in peripheral blood (B) were estimated at the indicated days postvaccination and represented as standard box-and-whiskers diagrams with individual values represented by dots. NoS, number of spots estimated from ELISPOT (see Materials and Methods for details). **1 × 10−3 < p ≤ 1 × 10−2, ****p ≤ 1 × 10−4. ns (not significant), 5 × 10−2 < p.

FIGURE 2.

Characteristics of the different clusters of participants. (A–D) For each cluster, receptor-binding domain (RBD)-specific IgG titers (A), frequencies of S protein–specific T cells (B), and virus-neutralizing activity (VNA) in serum against B.1.1.1 (C) and B.1.617.2 (D) SARS-CoV-2 variants were estimated as described in the Materials and Methods section and represented as standard box-and-whisker diagrams with individual values represented by dots. Orange corresponds to cluster 1, green to cluster 2, red to cluster 3. NoS, number of spots estimated from ELISPOT.

FIGURE 3.

Analysis of the virus-neutralizing activity in serum against B.1.1.1 and B.1.617.2 SARS-CoV-2 variants. (A) Dot plots for comparison between virus-neutralizing activity (VNA) in serum against B.1.1.1 and against B.1.617.2 for all patients at all time points. (B) Boxplots for ratio of VNA against B.1.1.1 to VNA against B.1.617.2 for all patients at different time points with both VNA against B.1.1.1 and VNA against B.1.617.2 above 0. (C) Left, Dot plot for pairwise comparisons of RBD-specific IgG titers and VNA against B.1.1.1 for all patients at all time points; the zone between markers from the right panel is shown in gray. Spearman c.c., Spearman correlation coefficient. Right, ROC curve for binary classifier separating patients into groups with VNA against B.1.1.1 ≥20 and <20 using RBD-specific IgG titers as a single input parameter. Two potential optimum thresholds are shown with markers. FPR, false positive rate; TPR, true positive rate. (D) Left, Dot plot for pairwise comparisons of RBD-specific IgG titers and VNA against B.1.617.2 for all patients at all time points; the zone between markers from the right panel is shown in gray. Spearman c.c., Spearman correlation coefficient. Right, ROC curve for binary classifier separating patients into groups with VNA against B.1.1.1 ≥20 and <20 using RBD-specific IgG titers as a single input parameter. Two potential optimum thresholds are shown with markers. FPR, false positive rate; TPR, true positive rate.