New COVID-19 sa-mRNA Results from CSL and Arcturus Therapeutics Demonstrate Longer Duration of Immunity Compared to Conventional COVID-19 mRNA Vaccine Booster

Global biotechnology leader CSL (ASX:CSL; USOTC:CSLLY) and Arcturus Therapeutics (Nasdaq: ARCT) today announced the results of a follow-up analysis of a Phase 3 study evaluating a booster dose of ARCT-154, the world's first approved self-amplifying messenger RNA (sa-mRNA) COVID-19 vaccine, compared to a conventional mRNA COVID-19 vaccine. ARCT-154 was administered at one-sixth the dose of Comirnaty (5 μg vs 30 μg, respectively).

The new analysis at 6 months post-vaccination shows that ARCT-154 induces a longer immune response as compared to Comirnaty for both the original Wuhan strain and Omicron BA.4/5 variant and an advantage in antibody persistence.

“These results further support sa-mRNA’s differentiating attribute to provide prolonged protection against COVID-19 at lower doses,” said Jonathan Edelman, M.D., Senior Vice President, Vaccines Innovation Unit, CSL. “Protecting the global public from viral respiratory diseases remains a top priority for us, and we look forward to continuing to collect and share data at the twelve-month post-booster mark.”

“This data, coupled with the initial Phase 3 results and approval in Japan late last year, show that this innovative vaccine technology has the potential to provide significant advancements over conventional mRNA vaccines including prolonged protection at lower doses,” said Pad Chivukula, Ph.D., Chief Scientific Officer of Arcturus Therapeutics.

ARCT-154 Six-Month Data Report

This randomized, double-blind, active-controlled study, conducted at 11 sites in Japan assessed the immunogenicity of ARCT-154 and Comirnaty at one, three- and six-months post-booster. Participants who displayed seropositivity for SARS-CoV-2 N-protein on Days 1, 29, 91 or 181 were considered indicative of recent COVID-19 infection and therefore, were progressively excluded from the analysis, leaving 332 and 313 participants in ARCT-154 and Comirnaty groups, respectively, eligible for inclusion at the six-month immunogenicity evaluation.

At baseline, participants in both groups had similar geometric mean titers (GMTs) surrogate virus neutralizing antibodies against Wuhan-Hu-1 strain (GMT ratio was 0.94 (95% CI 0.78-1.13)). One-month post-booster, the ARCT-154 group displayed a higher immune response with GMT of 5390 (95% CI 4899-5931, n = 378) compared to Comirnaty group with GMT of 3738 (95% CI 3442-4060, n = 367), and a GMT ratio of 1.44 (95% CI 1.27–1.64).