Meiji Holdings Co. Ltd. announced that a bivalent version of Kostaive®? (ARCT-2301: ancestral strain with the D614G mutation and omicron BA.4-5 subvariant), self-amplifying mRNA vaccine against COVID-19, met the primary endpoint in Phase III clinical study (jRCT2031230340) for booster vaccination which its subsidiary, Meiji Seika Pharma Co.

Ltd. conducted in Japan. In the Phase III clinical study, immunogenicity and safety of a bivalent version of Kostraive (ARCT -2301) was compared with COMIRNATY®? RTU (Bivalent: Ancestral strain and Omicron BA.4- 5 subvariant) in healthy Japanese adults aged 18 years or older previously immunized with three to five doses of mRNA COVID-19 vaccine.

Since non-inferiority of ARCT-2301 to COMIRNATY (BA.4/5) was confirmed both in the geometric mean titer (GMT) ratio and seroresponse rate (SRR) difference of neutralizing antibodies against SARS-CoV-2 (Omicron strain BA.4/5), the primary endpoint of the study was achieved. In addition, the superiority of ARCT-2301 To COMIRNATY (BA.,4/5) was confirmed for both SARS-CoV- 2 (Omicron strain BA.,4/5 and Wuhan strain). There were no causally-associated severe or serious adverse events with ARCT-2301.

These results support immunogenicity and safety of Kostaive®?'s self-amplifying mRNA platform enable Meiji Seika Pharma's timely release of update version of Kostaive®®? against novel variants of concern in 2024 in Japan. Meiji Seika Pharma conducted the study in collaboration with Arcturus Therapeutics and under its exclusive partnership with CSL Seqirus for the distribution of Kostaive®?

in Japan.