Arcturus reports positive results for sa-mRNA COVID boosters in phase 1/2 trial

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Amid a shrinking COVID-19 vaccine market, Arcturus Therapeutics is forging ahead with its mRNA candidate, revealing promising early data demonstrating its ability to stimulate the immune system. The biotech firm announced positive results from a small phase 1/2 trial involving three iterations of its self-amplifying mRNA (sa-mRNA) vaccines. The trial included 36 previously vaccinated participants in the US and Singapore, who were divided into groups receiving one of three Arcturus vaccines: targeting the ancestral strain, the B.1 variant with the D614G mutation, or the Beta variant. The study did not include a placebo control group.

Among the vaccine recipients, those who received the B.1-variant targeting booster (ARCT-154) exhibited the most robust response, with a 36.7 geometric mean fold rise (GMFR) in antibody levels—a measure of the increase in antibodies before and after vaccination. Participants who received the ancestral strain booster (ARCT-021) and Beta variant booster (ARCT-165) achieved GMFRs of 20 and 23.5, respectively. Notably, ARCT-154 elicited a broad and cross-neutralizing immune response that persisted for up to one year without requiring an additional shot. While the company provided limited details on the safety profile, it described side effects as mild or moderate, with low rates of related or severe adverse events.

“Current mRNA technologies provide effective initial immunogenicity against COVID-19, but the results of this study show that our sa-mRNA vaccine platform can offer improvements in duration and breadth of protection against new and emerging variants. We are proud of the role Arcturus has played, collaborating with CSL, in advancing sa-mRNA vaccine development.”

– Igor Smolenov, Chief Development Officer, Arcturus

Arcturus, in collaboration with CSL Behring, recently submitted an application to European regulators seeking approval for ARCT-154 as a new COVID-19 vaccine. Phase 3 trial data demonstrated that the vaccine had an efficacy rate of 56.6% against symptomatic COVID-19 and 95.3% against severe COVID-19. In a separate phase 3 booster trial, ARCT-154 met non-inferiority criteria when compared to Pfizer’s Comirnaty for protection against the ancestral strain.

While Arcturus has gained prominence for its COVID-19 vaccine endeavors, the company is also advancing clinical-stage treatments for ornithine transcarbamylase (OTC) deficiency and cystic fibrosis. It’s worth noting that Arcturus had previously collaborated with CureVac on the OTC medication, but the rights were returned to Arcturus in 2019.

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