Arcturus’ COVID-19 Vaccine Candidate Meets Primary Endpoint in Phase 3 Study


ARCT-154 demonstrates 95% efficacy overall for prevention of severe disease, including related deaths.

Arcturus Therapeutics Holding Inc announced positive topline data from an ongoing phase 1/2/3 trial evaluating ARCT-154, an mRNA vaccine candidate that aims to prevent COVID-19.

“We are very pleased with these results and to see ARCT-154 providing protection against symptomatic COVID-19 and almost complete protection against severe disease in a placebo-controlled vaccine efficacy study,” Joseph Payne, president and CEO of Arcturus Therapeutics, said in a statement.

The ongoing trial included more than 19,000 participants in Vietnam and included individuals who were at high risk for severe complications related to a COVID-19 infection.

The results from the efficacy analysis have been submitted to the Vietnam Ministry of Health by Vinbiocare and shared with Arcturus along with the filing. The additional efficacy data complements the data under review by the Vietnam Ministry of Health for a potential emergency use authorization of the vaccine candidate.

The phase 3 efficacy proportion of the study included more than 16,000 individuals. The evaluation of the efficacy showed that the study met its primary endpoint of prevention of virologically confirmed COVID-19 infection.

The data provided by Vinbiocare also showed that 2 5-mcg doses of ARCT-154 demonstrated 55% vaccine efficacy for protection against COVID-19, according to an analysis of cases between 7 and 56 days after completion of the 2-dose series.

The cases of COVID-19 infection in individuals that were detected coincided with an outbreak in Vietnam between December 2021 and February 2022, when the delta and omicron variants were prevalent.

Meanwhile in the study, the key secondary endpoint of severe COVID-19 infections, including COVID-19-related deaths, were analyzed and included 43 cases in the analysis.

Investigators found that 41 cases occurred in the placebo arm, and the other 2 were in the ARCT-154 arm, demonstrating that the estimated vaccine efficacy was approximately 95% against severe COVID-19 infection.

There were 9 COVID-19-related deaths in the placebo arm and just 1 in the ARCT-154 arm. The 1 death in the ARCT-154 arm occurred in an older individual who was at an increased risk of severe COVID-19.

The safety data showed that the incidence of adverse events (AEs) in the ARCT-154 arm and the placebo arm were comparable. There were no cases of myocarditis or pericarditis.

However, investigators noted that the sample was not large enough to observe these events, because of the rare occurrence of these AEs.

AEs were recorded by the individuals in the study for 7 days following each vaccination. Investigators found that AEs in the ARCT-154 arm were generally mild or moderate in severity. The frequency and severity of the AEs also did not increase with the second dose of the vaccine.

Furthermore, most AEs were resolved within the 7-day window.

The study also met the immunogenicity primary endpoint, with a 98.4% 4-fold seroconversion for the ancestral strain, which was measured by surrogate virus neutralizing test 28 days after the second dose of the vaccine candidate.

Arcturus will continue to examine the vaccine candidate and plans to have a study evaluating it in a booster dose, which will include about 2400 individuals.


Arcturus announces self-amplifying COVID-19 mRNA vaccine candidate ARCT-154 meets primary efficacy endpoint in phase 3 study. Business Wire. News release. April 20, 2022. Accessed April 21, 2022.

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