Researchers Announce Results of New COVID-19 sa-mRNA Vaccine


The findings suggest that 6 months after vaccination with ARCT-154, individuals had a longer immune response.

New study findings announced updated results from a follow-up analysis of a phase 3 study that evaluated the ARCT-154 booster dose. Researchers reported that ARCT-154 displayed a longer immune response 6 months prior to vaccination to prevent infection of the Wuhan strain and Omicron BA.4/5.

Doctor hands holding a vaccine bottle and syringe,beginning of worldwide mass vaccination for coronavirus COVID-19,influenza or flu,world immunization concept. Selective focu - Image credit: Aron M - Austria |

Image credit: Aron M - Austria |

The study authors noted that ARCT-154 is the first approved self-amplifying messenger RNA (sa-mRNA) COVID-19 immunization. The difference between mRNA and sa-mRNA vaccines is self-amplification, and sa-mRNA vaccines can help the body make more mRNA and protein to increase the immune system response— both providing protection against infectious disease.

"These results further support sa-mRNA's differentiating attribute to provide prolonged protection against COVID-19 at lower doses," said Jonathan Edelman, MD, Senior Vice President, Vaccines Innovation Unit, CSL, in a press release. "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 12-month post-booster mark."

ARCT-154 was compared to Comirnaty (Pfizer) and was administered at one-sixth of the dose in a randomized, double-blind, active-controlled study that was conducted in Japan at 11 sites, according to study authors.

Participants were randomly assigned to receive either ARCT-154 (N = 332) or Comirnaty (N = 313) and were assessed at month 1, 3, and 6 prior to receiving either booster vaccine.

The study authors noted that at the start of the study, individuals in both groups displayed comparable geometric mean titers (GMTs), which were defined as “surrogate virus neutralizing antibodies against Wuhan-Hu-1 strain.” However, in the 1-month analysis, researchers found that individuals that received ARCT-154 had a higher immune response compared to Comirnaty, with a GMT of 5390 versus 3738.

In the 3-month follow-up, the ARCT-154 group GMTs were 5928, whereas the Comirnaty group GMTs were 2899. The researchers found that the GMTs beside the Wuhan-Hu-1 strain remained higher 180 days after the ARCT-154 booster, compared to 28 days after the Comirnaty booster.

The study authors noted that the immunogenicity displayed similar patterns along with a decline in the Omicron BA.4/5 strain. Titers were stable or increased between days 29 and 91 among 128 individuals in the ARCT-154 group, compared to 36 individuals in the Comirnaty groups.

"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, PhD, Chief Scientific Officer of Arcturus Therapeutics, in a press release.

The findings suggested that 6 months after vaccination with ARCT-154, individuals had a longer immune response.


New COVID-19 sa-mRNA Results from CSL and Arcturus Therapeutics Demonstrate Longer Duration of Immunity Compared to Conventional COVID-19 mRNA Vaccine Booster. PR Newswire. News release. February 5, 2024. Accessed February 8, 2024.

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