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Metadata

Name
Immunogenicity and Safety of Heterologous and Homologous Boosting With ChAdOx1-S and CoronaVac or a Formulation of SCB-2019 (COVID-19)
Repository
ClinicalTrials.gov
Identifier
clinicaltrials:NCT05087368
Description
SARS-CoV-2 is a highly transmissible and pathogenic coronavirus that emerged in late 2019 and
has caused a pandemic of acute respiratory disease, collectively called coronavirus
disease-19 (COVID-19). SARS-CoV-2 has a high transmission rate, and severe cases of COVID-19
require admission to hospital intensive care units with the need for mechanical ventilation
and associated high mortality. Currently cases continue to rise in many countries as the
'second and third waves' of SARS-CoV-2 infection evolve.

The authorized vaccines and most vaccines in development are focused on the major antigenic
target of the virus, the SARS-CoV-2 spike (S) protein. Authorization was granted in Brazil by
ANVISA for the Fiocruz/Oxford-AstraZeneca ChAdOx1-S COVID-19 vaccine as a 2-dose homologous
vaccination regimen, 28- to 84-days apart. Emergency Use Authorization (EUA) was also granted
for Sinovac Biotech's CoronaVac vaccine as a 2-dose homologous vaccination regimen, 28 days
apart. Further vaccines, using different platforms are approved or expected to be approved
for use against SARS-CoV-2. Most of the vaccines are expected to be authorized as 2-dose,
homologous vaccination series.

SCB-2019 is Clover's adjuvanted recombinant SARS-CoV-2 trimeric S-protein subunit vaccine.
The SCB-2019 antigen includes SARS-CoV-2 S protein as a trimer fused to Trimer-Tag and is
produced in Chinese hamster ovary cells (CHO). SCB-2019 preserves the native trimeric
structure of S-protein in the prefusion form and induces neutralizing antibodies to
SARS-CoV-2. Trimer-Tag is derived from the fully-human C-propeptide domain of pro-collagen
and is capable of self-trimerization, thus fusing any biologically-active proteins in-frame
with Trimer-Tag. The resulting fusion proteins expressed in mammalian cells are secreted as
disulfide bond-linked homotrimers.

The immunogenicity and safety of different dose levels (3, 9, and 30 ?g) SCB-2019 vaccine,
administered as 2-dose regimen 21-days apart was assessed in a phase 1 clinical study. All
dose levels were well-tolerated and induced neutralizing antibodies against S protein of the
SARS-CoV-2 virus. Based on the results of that study, Clover selected 30 ?g of SCB-2019 in
combination with the CpG 1018/alum adjuvant system for further evaluation in the phase 2/3
clinical program as having the most favorable benefit/risk profile. The pivotal study
(CLO-SCB-2019-003) included approximately 30,000 healthy participants and individuals with
stable pre-existing chronic medical conditions, is being conducted in multiple countries,
including in Brazil. The primary purpose of that study (CLO-SCB-2019-003) is to demonstrate
the safety and efficacy of SCB-2019 in the prevention of COVID-19. The study showed efficacy.

Heterologous boost vaccinations using different platforms may elicit immune responses of
greater magnitude and breadth than can be achieved by priming or boosting with the same
vaccine (He et al, 2021, Spencer et al., 2021). Also, given the anticipated challenges of
vaccinating large proportions of the population, especially with respect to supply,
out-of-stock situations, and potential misadministration, it is important for policy makers
to have data on flexible vaccination schedules, where the third dose might be different from
the priming platform. Protein-based adjuvanted vaccines have the advantage of being from a
known and licensed technology that can produce high quantities of vaccine. Protein-based
adjuvanted vaccines have also been shown to be highly immunogenic, both in the context of
COVID-19 (Keech 2020; Richmond 2021) and other licensed vaccines (Skwarczynski 2016).

The purpose of this study is to compare the immunogenicity and safety of heterologous and
homologous booster schedules in individuals who received ChAdOx1-S or CoronaVac vaccination
previously. The study will be performed in 2 stages - Stage 1 will serve to down-select one
of the SCB-2019 formulations for boosting. Stage 2 will compare homologous and heterologous
booster regimens in individuals who have received a 2-dose primary vaccination series of
either ChadOx1-S or of CoronaVac.
Data or Study Types
clinical trial
Keywords
Covid19, Vaccines, Immunogenicity
Source Organization
Unknown
Access Conditions
available
Year
2021
Access Hyperlink
https://clinicaltrials.gov/ct2/show/NCT05087368

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