Longitudinal Follow-Up of the Immunity to SARS-CoV-2 in Health Care Workers in Argentina: Persistence of Humoral Response and Neutralizing Capacity after Sputnik V Vaccination

Abstract

SARS-CoV-2 vaccine protection has encountered waning of immune response and breakthrough infections. The hybrid immune response generated by the combination of vaccination and infection was shown to offer higher and broader protection. Here, we present a seroprevalence study of anti-SARS-CoV-2 spike/RBD IgG in 1,121 health care workers immunized with Sputnik V and a follow-up of humoral response at 2 and 24 weeks postvaccination (wpv), including neutralizing antibody response (NAT) against ancestral, Gamma, and Delta variants. The first seroprevalence study showed that among 122 individuals with one dose, 90.2% were seropositive versus 99.7% seropositivity among volunteers with the complete two-dose regimen. At 24 wpv, 98.7% of the volunteers remained seropositive, although antibody levels decreased. IgG levels and NAT were higher in individuals that had acquired COVID-19 previous to vaccination than in naive individuals at 2 and 24 wpv. Antibody levels dropped over time in both groups. In contrast, IgG levels and NAT increased after vaccine breakthrough infection. At 2 wpv, 35/40 naive individuals had detectable NAT against SARS-CoV-2 Gamma and 6/40 against Delta. In turn, 8/9 previously infected individuals developed a neutralizing response against SARS-CoV-2 Gamma and 4/9 against Delta variants. NAT against variants followed a trajectory similar to NAT against ancestral SARS-CoV-2, and breakthrough infection led to an increase in NAT and complete seroconversion against variants. In conclusion, Sputnik V-induced humoral response persisted at 6 months postvaccination, and hybrid immunity induced higher levels of anti-S/RBD antibodies and NAT in previously exposed individuals, boosted the response after vaccination, and conferred wider breadth of protection. IMPORTANCE Since December 2020, Argentina has begun a mass vaccination program. The first vaccine available in our country was Sputnik V, which has been approved for use in 71 countries with a total population of 4 billion people. Despite all the available information, there are fewer published studies on the response induced by Sputnik V vaccination compared to that of other vaccines. Although the global political context has paralyzed the verification by the WHO of the efficacy of this vaccine, our work aims to add new clear and necessary evidence to Sputnik V performance. Our results contribute to general knowledge of the humoral immune response developed by vaccines based on viral vector technology, highlighting the higher immune protection conferred by hybrid immunity and reinforcing the importance of completing vaccination schedules and booster doses to maintain adequate antibody levels.

Keywords: SARS-CoV-2; Sputnik V; humoral immune response; hybrid immunity; vaccination.

FIG 1

Design and main seropositivity results of anti-S/RBD SARS-CoV-2 IgG seroprevalence study. Seroprevalence study was carried out in a cohort of 1,121 individuals vaccinated with Sputnik V. First, the humoral immune response of individuals having received one (2 weeks after first dose, n = 122) or two doses (1 to 2 weeks after second dose, n = 999) after the beginning of the vaccination campaign was evaluated. A second seroprevalence study was carried out at 24 weeks after completion of the two-doses vaccination schedule (24 wpv) and included 538 fully vaccinated individuals from the initial cohort. Three hundred and eighty individuals with paired samples obtained both at 2 and 24 wpv were selected for further analysis and divided according to their COVID status (i) without a diagnosis of COVID-19 prior or during the study period (n = 271; Non-COVID); (ii) with confirmed COVID-19 diagnosis prior to the start of the vaccination schedule (COVID-PreV; n = 74); and (iii) with breakthrough infections (confirmed COVID-19 diagnosis between 2 and 24 wpv, COVID-PostV; n = 35). Finally, 49 of these individuals were selected for neutralizing antibodies (Nab) analysis.

FIG 2

Total IgG antibody levels against Spike/RBD of SARS-CoV-2 after Sputnik V vaccination. The levels of IgG antibodies against the ectodomain of the original Wuhan spike protein and RBD were measured by COVIDAR IgG ELISA, and quantification was carried out calculating the PI values (range from 1 to 10) according to manufacturer’s instructions. (A) Serum samples were collected 2 weeks after application of the first dose (1D) (n = 122) and 1 to 2 weeks after second dose (2D) (n = 999) of Sputnik V. (B) Antibody levels were evaluated in 380 individuals after 2 and 24 weeks after completion of the vaccination schedule (wpv). (C) Individual evolution of total IgG anti-Spike/RBD levels at 2 and 24 wpv. Individual PI values and geometric mean with 95%CI are shown. Mann-Whitney U test was used for analysis of the total IgG antibody levels. Wilcoxon matched-pair test was used for individual longitudinal analysis of the total IgG antibody levels. Statistical significance is shown with the following notations: ****, P < 0.0001.

FIG 3

Evolution of total anti-Spike/RBD IgG and neutralizing antibody levels against ancestral SARS-CoV-2 after Sputnik V vaccination according to COVID-19 diagnosis. Sera collected at 2 and 24 wpv were obtained from a cohort of 380 individuals at 2 and 24 weeks after completion of the vaccination schedule (wpv) with Sputnik V. Cohort was differentiated into individuals (i) without a diagnosis of COVID-19 prior to vaccination or during the study period (Non-COVID; black dots); (ii) with confirmed COVID-19 diagnosis prior to the start of the vaccination schedule (COVID-PreV; orange dots); and (iii) with confirmed COVID-19 diagnosis after 2wpv (COVID-PostV; purple dots). (A) Anti-Spike/RBD IgG levels were evaluated in Non-COVID (n = 271), COVID-PreV (n = 74), and COVID-PostV (n = 35). Individual PI values and geometric mean with 95%CI are shown. (B) Neutralizing titers (NT) were defined as the highest serum dilution without any viral cytopathic effect on the monolayer using a replicating SARS-CoV-2. NT were evaluated in Non-COVID (n = 29); COVID-PreV (n = 9); and COVID-PostV (n = 9). Individual NT values and geometric mean with 95%CI are shown. Samples with NT below 8 (limit of detection, LOD) were set at 1 to calculate GMNTs. Pie charts illustrate the percentage of samples that resulted positive for neutralizing antibodies (NT ≥ 8). Tables next to each graph indicate the corresponding GM, 95%CI values, and GM fold change of 24 versus 2 wpv. Wilcoxon matched-pair test was used for longitudinal analysis of total IgG antibody levels and neutralizing titers. For nonpaired samples, the Mann-Whitney U test was used. Statistical significance is shown with the following notations: ****, P < 0.0001; ***, P < 0.001; **, P < 0.01; *, P < 0.05; ns, not significant.

FIG 4

Neutralizing titers against SARS-CoV-2 Gamma and Delta VOCs after Sputnik V vaccination. Neutralizing titers (NT) were defined as the highest serum dilution without any cytopathic effect on the monolayer using a replicating SARS-CoV-2 Gamma and Delta. Sera collected at 2 and 24 weeks after completion of the vaccination schedule (wpv) with Sputnik V were used. (A and B) Cohort was differentiated into the following individuals: (i) Non-COVID, black dots (n = 29); (ii) COVID-PreV, orange dots (n = 9); and (iii) COVID-PostV, purple dots (n = 9). Sera were evaluated against (A) SARS-CoV-2 Gamma and (B) Delta. Individual NT values and geometric mean with 95%CI are shown. Tables next to each graph indicate the corresponding GMNT, 95%CI values, and GMNT fold change of 24 versus 2 wpv. Pie charts illustrate the percentage of samples that resulted positive for neutralizing antibodies (NT ≥ 8). (C and D) NT at (C) 2 wpv or (D) 24 wpv of sera from 29 naive individuals. NT for each sample is shown, and lines connect the same sample. Pie charts illustrate the percentage of samples that resulted positive for neutralizing antibodies (NT ≥ 8). Samples with NT below 8 (limit of detection, LOD) were set at 1 to calculate GMNTs. Wilcoxon matched-pair test was used for longitudinal analysis of the neutralizing titer. For nonpaired samples analysis, the Mann-Whitney U test was used. Statistical significance is shown with the following notations: ****, P < 0.0001; *, P < 0.05; ns, not significant.

FIG 5

Correlation between anti-S/RBD antibodies and neutralizing antibodies against ancestral SARS-CoV-2 after Sputnik V vaccination in naive individuals. Sera of 29 naive individuals collected at 2 and 24 weeks after completion of the vaccination schedule (wpv) with Sputnik V were used. (A) Correlation between IgG anti-S/RBD (PI) tested with COVIDAR and Anti-S/RBD antibodies tested with Elecsys Anti-SARS-CoV-2 S assay (Roche) (n = 56). Samples with PI of ≥10 were set at PI = 10, and samples with antibody titers above 250 U/mL were set at 250. (B) Correlation of NT with IgG anti-S/RBD (PI) tested with COVIDAR IgG (n = 58). Samples with PI of ≥10 were set at PI = 10. (C) Correlation of NT with anti-S/RBD antibody titers tested with Elecsys assay (Roche) (n = 56). Samples with antibody titers above 250 U/mL were set at 250. NT below 8 were set at 1. LOD indicates the limit of detection of neutralizing antibodies. Correlation was analyzed by Spearman’s r test. P < 0.05 was considered significant.