The fourth COVID-19 vaccine dose increased the neutralizing antibody response against the SARS-CoV-2 Omicron (B.1.1.529) variant in a diverse Brazilian population

Abstract

Most of the original immunization regimens against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were composed of two doses, followed by a subsequent third booster dose to control the Omicron variant and hence coronavirus disease 2019 (COVID-19). However, most data generated regarding the fourth dose were not based on the general population. Therefore, this study aimed to verify the effect of the fourth COVID-19 vaccine dose in a diverse Brazilian population. This retrospective observational study was conducted between May and September 2022. We gathered data on the vaccine regimens and COVID-19 serologic status from 266 healthy volunteers who received three or four vaccine doses, as well as COVID-19 diagnosis and viral genome sequencing from 457 patients with flu-like symptoms. In addition, we conducted immunoinformatic analysis to assess the conserved epitopes in the locally circulating viruses. We showed that the fourth dose did not increase the serum levels of antiviral antibodies, as measured by enzyme-linked immunosorbent assay. However, it significantly increased neutralizing antibody (NAb) titers against the Omicron variant. All viral sequences generated in this study were Omicron subvariants, mainly B.A.5.1. Notably, most NAb epitopes present in the wild-type SARS-CoV-2 were not detected among the circulating Omicron subvariants. None of the volunteers who received the third or fourth doses presented COVID-19 for at least 1 year before the study period. Altogether, these results indicate that the fourth vaccine dose increases the serum levels of NAbs that recognize highly conserved epitopes in Omicron subvariants. IMPORTANCE Several additional COVID-19 vaccine doses were administered in the Brazilian population to prevent the disease caused by the B.1.1.529 (Omicron) variant. The efficacy of a third dose as a booster is already well described. However, it is important to clarify the humoral immune response gain induced by a fourth dose. In this study, we evaluate the effect of the fourth COVID-19 vaccine dose in a diverse Brazilian population, considering a real-life context. Our study reveals that the fourth dose of the COVID-19 vaccine increased the neutralizing antibody response against SARS-CoV-2 Omicron and significantly contributed in the reduction of the disease caused by this variant.

Neutralizing antibody response after immunization with a COVID‐19 bivalent vaccine: Insights to the future

“…Although PRNT, and FRNT are considered golden standard, the CPE‐VNT has shown to be particularly useful for studying larger sets of samples 18,26,27 . The same technique has been used in our previous studies 13,14 and we preferred not to change the methodology in the present study. Nevertheless, we present robust statistical analysis that support our main statements and conclusions.…”

“…are considered golden standard, the CPE-VNT has shown to be particularly useful for studying larger sets of samples. 18,26,27 The same technique has been used in our previous studies 13,14 and we preferred not to change the methodology in the present study.…”

“…The CPE‐VNT assay was performed in a BSL3 laboratory, in accordance with the WHO recommendations. NAb titers against SARS‐CoV‐2 variants were measured as described previously 13,14,18 . Briefly, cell monolayers (5 × 10 4 Vero CCL‐81 cells/well) in 96‐well culture plates were exposed to 1 × 10 3 TCID50/mL of SARS‐CoV‐2 Wuhan strain—WT or Omicron subvariants (BA.1, FE.1.2, BQ.1.1) that were previously incubated with 1:20–1:1280 twofold diluted, heat‐inactivated human serum samples, in a final volume of 150 µL.…”

“…The group that received the bivalent vaccine had an average time interval of 7.92 ± 1.12 months between the last two doses, and a 0.4 ± 0.16 months' interval between the last dose and sampling. In addition, none of the participants of this study were infected with SARS‐CoV‐2 for at least 1 year before the study period, as determined by the lack of registered evidence of illness (COVID‐19), confirmed by RT‐qPCR and presentation of symptoms, as previously described 13,14 . Demographic information (Supplementary Material ) as well as serum samples were collected.…”

“…In addition, none of the participants of this study were infected with SARS-CoV-2 for at least 1 year before the study period, as determined by the lack of registered evidence of illness (COVID- 19), confirmed by RT-qPCR and presentation of symptoms, as previously described. 13,14 Demographic information (Supplementary Material S1) as well as serum samples were collected. An enzyme linked immunosorbent assay (ELISA) was carried out to measure the serum levels of antibodies capable of recognizing the S and the nucleocapsid (N) proteins, as previously described.…”