Safety and efficacy of SCB-2019 COVID vaccine candidate as a ChAdOx1-S booster
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In a current examine posted to the medRxiv* pre-print server, researchers evaluated the immunogenicity of booster doses of alum-adjuvanted SCB-2019 vaccine candidate’s three formulations. They examined this novel vaccine candidate in Brazilian adults primed with the ChAdOx1-S coronavirus illness 2019 (COVID-19) vaccine between November 2021 and March 2022.

Study: Homologous and heterologous boosting of the ChAdOx1-S1-S COVID-19 vaccine with the SCB-2019 vaccine candidate: a randomized, observer-blinded, managed, section 2 examine. Image Credit: PhotobyTawat / Shutterstock


Many low- and middle-income nations (LMICs), together with Brazil, are utilizing viral vector-based vaccines (e.g., ChAdOx1-S1) for vaccinating their populations. Implementing vaccination campaigns with booster photographs may assist broaden the immune response amid waning immunity following vaccination and modifications within the antigenic goal with new waves of the COVID-19 pandemic.

SCB-2019 is a novel recombinant extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S)-protein vaccine (S-Trimer) whose two 30 μg doses demonstrated 67.2% efficacy in opposition to COVID-19 within the SPECTRA section II/III trial. It confirmed an efficacy of 78.7%, 91.8%, and 58.6% in opposition to SARS-CoV-2 Delta, Gamma, and Mu variants.

About the examine

In the current examine, researchers investigated using SCB-2019 in heterologous booster regimens in contrast with homologous boosters. They aimed to pick out the optimum SCB-2019 formulation for the heterologous boosting of people vaccinated with the ChAdOx1-S1 vaccine. The group additionally assessed the protection and immunogenicity of the three formulations of SCB-2019.

The first two formulations had a 9 μg dose of SCB-2019 and alum with and with out the CpG oligodeoxynucleotides (CpG-1018) adjuvant to research potential dose-sparing. The third formulation comprised the usual 30 μg dose with CpG-1018 and alum.

The 120 eligible contributors have been male or feminine adults over 18 years vaccinated with the ChAdOx1-S1-S vaccine six months (± 4 weeks) earlier than enrolment and complied with all of the examine procedures and necessities, together with scheduled visits and laboratory exams. At the enrolment, the researchers randomly allotted all of the examine contributors 1:1:1:1 to obtain one of many three SCB-2019 formulations.

Trained unblinded vaccine directors ready the ultimate vaccine formulations. They administered the vaccine intramuscularly (i.m.) to all of the examine contributors utilizing one mL tuberculin syringes. The group monitored the contributors who acquired their assigned vaccination for half-hour for any instant reactions. Later, the participant self-reported prevalence of solicited native reactions, equivalent to ache, erythema, and swelling on the injection website, and systemic adversarial occasions, if any. They additionally reported any critical adversarial occasions (SAE), or medically attended adversarial occasions (MAAE) as much as day 29 of the follow-up interval.

The researchers collected serum samples earlier than vaccination and on days 15 and 29 to evaluate the immune responses however examined samples from solely these contributors who acquired the right vaccination and had no protocol deviation. They used an enzyme-linked immunosorbent assay (ELISA) to measure immunoglobulin G (IgG) antibodies in opposition to SCB-2019 S-protein. Likewise, they measured the inhibition of binding of S-protein to the human angiotensin-converting enzyme 2 (ACE2).

The group expressed ELISA antibody titers in opposition to SCB-2019 S-protein as geometric imply titers (GMT), geometric mean-fold rise in titers over baseline (GMFR), and seroconversion charges (SCR). In the examine contributors with a baseline titer above the decrease restrict of quantitation (LLOQ), a four-fold improve in post-vaccination titer indicated seroconversion. Conversely, in those that didn’t have detectable exercise at baseline, a post-vaccination titer greater than four-fold the LLOQ indicated seroconversion.

Booster vaccination responses proven as geometric imply titers (95% CI) of ELISA antibodies in opposition to SCB-2019 (panel A) and ACE2 (panel B) at Days 15 and 29 after vaccination. Geometric mean-fold rises (GMFR) from Day 1 (95% CI) are proven with ANCOVA p values of variations between Groups 1-3 (SCB-2019) and Group 4 (ChAdOx1-S): * p <0.05; ** p < 0.01, *** p < 0.001). Numbers in columns are n values per group.

Study findings

The normal formulation containing 30 μg SCB-2019 with the toll-like receptor 9 (TLR-9) agonist CpG-1018 and alum confirmed the most effective booster response. This formulation demonstrated acceptable reactogenicity, akin to that noticed within the SPECTRA examine. Moreover, it was protected and extremely efficacious as a heterologous booster following main vaccination.

Additionally, the 30 μg SCB-2019 dose elicited a considerably increased immune response in opposition to SARS-CoV-2 S-protein and inhibited the binding of S-protein to the ACE2 receptor, higher than the homologous ChAdOx1-S vaccine. Furthermore, it confirmed higher neutralizing exercise in opposition to 4 SARS-CoV-2 variants. The neutralizing exercise in opposition to the SARS-CoV-2 Omicron variant was considerably decrease 15 days after homologous boosting with SCB-2019+CpG+alum formulations. However, titers in opposition to Omicron waned barely within the SCB-2019 teams by day 29.

Booster vaccination responses proven as geometric imply neutralizing titers (with 95% CI) in opposition to the indicated SARS-CoV-2 variants 15 days after vaccination. Differences in GMTs of Groups 1-3 vs. Group 4 at Day 15 have been examined by ANCOVA; * p < 0.05; ** p < 0.01; *** p < 0.001.


Overall, the 30 μg SCB-2019 formulation adjuvanted with CpG-1018 and alum was protected and well-tolerated in these beforehand primed with ChAdOx1-S. Importantly, it was immunologically more practical when given as a heterologous booster.

Previous research have proven that the immune response to a heterologous second messenger ribonucleic acid vaccine after a main dose of ChAdOx1-S was extra fast than the homologous vaccination. Therefore, additional investigation is warranted to find out the distinction within the kinetics of the immune response to the homologous booster of the SCB-2019 vaccine formulation.

*Important discover

medRxiv publishes preliminary scientific reviews that aren’t peer-reviewed and, subsequently, shouldn’t be thought to be conclusive, information medical follow/health-related conduct, or handled as established info.v1

Journal reference:

  • Homologous and heterologous boosting of the ChAdOx1-S1-S COVID-19 vaccine with the SCB-2019 vaccine candidate: a randomized, observer-blinded, managed, section 2 examine, Sue Ann Costa Clemens, Eveline Pipolo Milan, Eduardo Sprinz, Jose Cerbino Neto, Filippo Pacciarini, Ping Li, Hui-Ling Chen, Igor Smolenov, Andrew Pollard, Ralf Clemens, medRxiv pre-print 2022,  DOI:, material/10.1101/2022.05.31.22275010

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