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. 2023 Nov 2;228(9):1253-1262.
doi: 10.1093/infdis/jiad262.

Superior Boosting of Neutralizing Titers Against Omicron SARS-CoV-2 Variants by Heterologous SCB-2019 Vaccine vs a Homologous Booster in CoronaVac-Primed Adults

Camilo C Roa Jr  1 , Mari Rose A de Los Reyes  2 , Eric Plennevaux  3 , Igor Smolenov  4 , Branda Hu  4 , Faith Gao  4 , Hannalyn Ilagan  4 , Donna Ambrosino  5 , George Siber  6 , Ralf Clemens  7
Affiliations

Superior Boosting of Neutralizing Titers Against Omicron SARS-CoV-2 Variants by Heterologous SCB-2019 Vaccine vs a Homologous Booster in CoronaVac-Primed Adults

Camilo C Roa Jr et al. J Infect Dis. .

Abstract

Background: We compared homologous and heterologous boosting in adults in the Philippines primed with 2 or 3 doses of CoronaVac, with recombinant protein vaccine, SCB-2019.

Methods: CoronaVac-immunized adults (18-72 years) received a homologous or heterologous full or half dose SCB-2019 booster. We assessed all neutralizing antibody (NAb) responses against prototype SARS-CoV-2 after 15 days and NAb against SARS-CoV-2 Delta and Omicron variants in subsets (30‒50 per arm). Participants recorded adverse events.

Results: In 2-dose CoronaVac-primed adults prototype NAb geometric mean titers (GMT) were 203 IU/mL (95% confidence interval [CI], 182-227) and 939 IU/mL (95% CI, 841-1049) after CoronaVac and SCB-2019 boosters; the GMT ratio (4.63; 95% CI, 3.95-5.41) met predefined noninferiority and post-hoc superiority criteria. After 3-dose CoronaVac-priming prototype NAb GMTs were 279 IU/mL (95% CI, 240-325), 1044 IU/mL (95% CI, 898-1213), and 668 IU/mL (95% CI, 520-829) following CoronaVac, full and half-dose SCB-2019 boosters, respectively. NAb GMT ratios against Delta and Omicron comparing SCB-2019 with CoronaVac were all greater than 2. Mild to moderate reactogenicity was evenly balanced between groups. No vaccine-related serious adverse events were reported.

Conclusions: Full or half dose SCB-2019 boosters were well tolerated with superior immunogenicity than homologous CoronaVac, particularly against newly emerged variants. Clinical Trials Registration. NCT05188677.

Keywords: COVID-19; CoronaVac; Delta; Omicron; SCB-2019; booster; immunogenicity; reactogenicity; recombinant protein; vaccine.

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Figures

Figure 1.
Figure 1.
Disposition of participants in safety set and per protocol immunogenicity sets in stages 1 and 2 of the study.
Figure 2.
Figure 2.
Immune responses in the 2 stages as geometric mean neutralizing titers (IU/mL) with 95% CI against prototype SARS-CoV-2 on day 1, before the indicated booster vaccinations, and day 15 in both stages. Numbers above columns show GMT values. GMT ratios (95% CI) by ANCOVA between SCB-2019 and CoronaVac groups are shown above; GMFR are shown below. Titers are expressed in IU/mL using the World Health Organization standard 21/234. Abbreviations: CI, confidence interval; GMFR, geometric mean fold rise; GMT, geometric mean titer; IU, international unit.
Figure 3.
Figure 3.
GMT (1/dilution) of neutralizing antibodies against prototype, Delta, and Omicron SARS-CoV-2 variants in subsets of stage 2 including fourth-dose CoronaVac (n = 50), full-dose (n = 49), and half-dose (n = 50) SCB-2019 study groups, with GMFR (95% CI) between days 1 and 15 indicated. For Omicron BF.7, BQ1.1.1, and XBB.1.5 subsets were 30 for fourth-dose CoronaVac (n = 30), full-dose SCB-2019 (n = 29), and half-dose SCB-2019 (n = 30), with GMFR (95% CI) between days 1 and 15 indicated below. Abbreviations: CI, confidence interval; GMFR, geometric mean fold rise; GMT, geometric mean titer.
Figure 4.
Figure 4.
Proportions of the 2 study groups with solicited local reactions and systemic adverse events (AEs) by highest severity.
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