On Sept. 27, 2023, Gritstone bio announced that it was awarded a contract by the Biomedical Advanced Research and Development Authority (BARDA) to conduct a Phase 2b comparative study evaluating Gritstone’s self-amplifying mRNA (samRNA) vaccine candidate containing Spike plus other viral targets to protect against COVID-19.

The contract will support Gritstone as it conducts a 10,000 participant, randomised Phase IIb double-blinded study. The study will compare the efficacy, safety, and immunogenicity of the company’s next-generation COVID-19 vaccine candidate with an approved vaccine. Gritstone reports that “preparations for the study are underway”, with the execution being “fully funded by BARDA”. It will take place in the US, in collaboration with the COVID-19 Prevention Network (CoVPN), which is a NIAID-supported network of trial sites based at Fred Hutchinson Cancer Centre.  

Gritstone explains that self-amplifying mRNA (samRNA) is “rapidly emerging” as a “well-tolerated, scalable, and widely applicable platform technology”. It can be used in multiple vaccines if the sequence of the antigen that is encoded in the vector RNA is changed. Like “traditional mRNA vaccines”, these vaccines use the host cell’s translation system to “convert mRNA” to protein target antigens, stimulating immunity. However, in contrast to traditional mRNA, samRNA “creates multiple copies of the antigen RNA once in the cell”, which is believed to be a possible factor in extending the “duration and magnitude of antigen expression”.