Gritstone Bio has reported interim results from an ongoing Phase 1 study evaluating the company’s self-amplifying mRNA (samRNA) vaccine as a boost against Covid-19 (CORAL-BOOST).

According to the US-based company, the results demonstrate that Gritstone’s samRNA vaccine candidate boosted immunity for at least 6 months in previously vaccinated older adults.

These are generally consistent with initial results from a separate Phase I study in previously unvaccinated subjects (CORAL-CEPI).

These results were first reported by Gritstone in October 2022.

“Publication of these results in Nature Communications supports the scientific rigor of our work and potential clinical utility of our next-generation vaccine platform for the prevention of infectious diseases, including coronaviruses, such as Covid-19,” said Andrew Allen, Chief Executive Officer of Gritstone.

“The published results are part of a rapidly growing body of evidence demonstrating the potential advantages of samRNA over first-generation Covid-19 vaccines, including extended antigen expression and dose sparing potential. It is clear that new technologies are needed to help prevent and manage future pandemics, and we believe the results we are seeing from our CORAL program represent a promising step forward in this endeavour.”

The company’s samRNA vector is based on a synthetic RNA molecule derived from a wild-type Venezuelan Equine Encephalitis Virus (VEEV) replicon with the goal of extending the duration and magnitude of immunogen expression to drive potent and durable immune responses. The samRNA is delivered in a lipid nanoparticle (LNP) formulation.

The Phase I CORAL-BOOST dose-escalation trial (NCT05148962) evaluated Gritstone's samRNA candidate (GRT-R910) in previously vaccinated healthy older adults.

Results demonstrated a favourable safety and tolerability profile in this vulnerable population.

Most adverse events (AEs) following dosing were mild to moderate and transient with no treatment-related serious AEs observed.

With respect to immunogenicity, neutralising antibody titers against ancestral Spike and variants of concern were boosted by the samRNA candidate, and contrasting to authorised vaccines, persisted through at least 6 months following the booster dose.

Furthermore, Gritstone's samRNA increased and potentially broadened functional Spike-specific T cell responses and primed T cell responses to conserved non-Spike epitopes.

The CORAL-BOOST trial is part of Gritstone’s CORAL program which currently includes three ongoing Phase I trials: CORAL-BOOST, which is evaluating one construct in a boost setting (following primary series of currently-approved Covid-19 vaccines); CORAL-CEPI (NCT05435027), which is evaluating multiple constructs in virus-naïve, convalescent, and HIV+ subjects in South Africa; and CORAL-NIH, which is being run by the National Institute of Allergy and Infectious Disease (NIAID) and is evaluating multiple constructs in previously vaccinated healthy volunteers.

According to GlobalData, there are over 800 Covid-19 vaccines in the pipeline, 42.6% of these are in the pre-clinical stage.

GlobalData is the parent company of Clinical Trials Arena.