COVID-19 S-Trimer vaccine (Sichuan Clover Biopharmaceuticals, Inc)

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 known as COVID-19. Given the relatively short duration of protection after vaccination or SARS-CoV-2 infection and the evolution of immune-evading strains, it is likely that the population will have to be repeatedly boosted until a "universal" Pan-Sarbecovirus vaccine is available.
SARS-CoV-2 protein subunit vaccine candidates have shown that, despite adjuvantation, their safety/reactogenicity profile seems to be preferable over mRNA or vectored vaccines, whilst inducing non-inferior immune responses (1,2).
In this regard, serious adverse events of special interest from mRNA vaccines seem to be have been substantially underestimated/underreported. In a preliminary analysis by an International consortium, the true incidence seems to be 1,250/million excess risk in vaccinees instead of the 1-2/million reported by the Department of Health and Human Services (3,4). Additionally, in a recent study, the Clover SCB-2019 protein subunit vaccine candidate has shown higher neutralizing antibodies titers against the omicron variant, when compared to an inactivated vaccine (data not published yet). Although Brazil has various vaccine platforms authorized for emergency use or licensed, such as mRNA vaccines, vector-based vaccines, inactivated vaccines, so far Brazil has no access to adjuvanted or non-adjuvanted protein-based vaccines.
This study will involve two vaccines registered in Brazil and a protein-based adjuvanted vaccine candidate, SCB-2019/Clover. Protein-based adjuvanted vaccines have the advantage of being from a known and licensed technology that can produce high quantities of vaccine at reasonable Costs of Goods. Protein-based adjuvanted vaccines have also been shown to be highly immunogenic, both in the context of COVID-19 (2,5) and other licensed vaccines (6), with long persistence of immunity and protection.
Over 80% of the Brazilian population above the age of 18 years have received a full primary vaccination and another 7% at least one dose of vaccine. The overall booster coverage is about 48% (64% of the adults) (7). Anvisa has authorized 1st and 2nd booster doses of various vaccines in line with the MoH policy which was last updated in March 2022. It can be speculated that, like in other geographies, a third booster will be recommended soon, especially to at risk populations and in the scenario of high circulation of the Omicron BA.5 strain.
This study will explore the immunogenicity, safety and reactogenicity of a booster dose of various platforms in fully primed individuals regardless of the number of booster doses they have received prior to the enrollment in the study.
This mimics the "real world scenario" at vaccination centers where individuals with different background vaccination schemes show up for "a booster". It would facilitate logistics of immunization substantially if vaccines for boosting, independent of the immunization status, could be interchangeable with respect to safety/reactogenicity and immunogenicity. This study will enroll fully-primed individuals (2 doses of either Pfizer mRNA or Oxford/AZ/Fiocruz or Sinovac/Butantan or 1 dose of Janssen vaccine) who have received their last vaccine dose at least 4 months prior to study entry and who have received either no booster, or 1 or 2 boosters. Individuals will be stratified in cohorts by number of boosters and then randomized to receive one of 3 booster vaccines (AstraZeneca/Fiocruz, Pfizer/Wyeth, SCB-2019/Clover).