Arcturus Therapeutics Holdings Inc. (the “Company”, “Arcturus”, Nasdaq: ARCT), a global late-stage clinical messenger RNA medicines company focused on the development of infectious disease vaccines and opportunities within liver and respiratory rare diseases, today announced the results of a phase 1/2 study showing that a booster dose of a novel, self-amplifying messenger RNA (sa-mRNA) vaccine against COVID-19 induces a robust, broadly cross-reactive, and durable immune response in adults that remains elevated through 12 months after vaccination. Three sa-mRNA vaccines were used in the study, which was presented as a poster at the European Scientific Working Group on Influenza's 9^th ESWI Influenza Conference in Valencia, Spain.

Messenger RNA (mRNA) vaccine technology protects against infectious diseases by instructing cells in the body to make a specific protein, stimulating the immune response, and leaving a blueprint to recognize and fight future infection. However, sa-mRNA also provides the body with instruction to make copies of the mRNA, amplifying the amount of protein made. This advanced technology has shown the potential to offer longer duration of immune response at considerably lower doses compared to conventional mRNA vaccines.

“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,” said Igor Smolenov, Chief Development Officer, Arcturus. “We are proud of the role Arcturus has played, collaborating with CSL, in advancing sa-mRNA vaccine development.”

CSL’s vaccine business, CSL Seqirus, is Arcturus’ global exclusive partner for the development of novel mRNA vaccines against SARS-CoV-2 (COVID-19), influenza and pandemic preparedness. CSL has a dynamic portfolio of lifesaving medicines, including those that treat hemophilia, hereditary angioedema (HAE) and immune deficiencies, vaccines to prevent influenza, and therapies in iron deficiency and nephrology.

“We are encouraged by the findings of the study, indicating the sa-mRNA platform’s potential to solve the challenge of mRNA vaccine waning immunity over time, and thereby provide prolonged protection at lower doses,” said Esther Heijnen, M.D., Vice President, Clinical Development, Vaccines Innovation Unit, CSL. “Our collaboration with Arcturus on advanced mRNA vaccines is another example of CSL’s relentless pursuit of disruptive innovation when public health and patients can benefit.”