Arcturus COVID-19 Vaccine Hits Mark in Phase III Trial


Arcturus Therapeutics announced positive Phase III trial results for its mRNA vaccine candidate, ARCT-154. ARCT-154 is intended to prevent COVID-19 caused by the SARS-CoV-2 virus.

The Phase I, II and III trials of ARCT-154 took place in Vietnam and enrolled over 19,000 adults, including those at high risk of severe complications from COVID-19. The Phase III portion of the study enrolled 16,000 patients and met its primary endpoint of preventing virologically confirmed COVID-19. Overall, the vaccine provided 55% efficacy for preventing symptomatic COVID-19 in those that received both doses in the series.

The key secondary endpoint of the trial was to evaluate if the vaccine protected against severe cases of COVID-19. ARCT-154 demonstrated a vaccine efficacy of 95% in protecting against severe cases, including fatal diseases. The vaccine trials took place during the Delta and Omicron variant surges in Vietnam, although Arcturus did not speculate on which variants the vaccine could potentially provide the most benefit against.

The incidence of unsolicited adverse events was comparable between the vaccinated and placebo groups with no incidences of myocarditis or pericarditis. Only one death was reported in the vaccinated group that was at risk for severe COVID-19.

Although the vaccine hit its primary endpoint, Arcturus’ stock dipped 9% because of low efficacy rates. Despite this, the company has submitted results from its efficacy analysis to the Vietnam Ministry of Health in conjunction with its collaborator, Vinbiocare. The additional efficacy data was provided to supplement a previously submitted data package for potential Emergency Use Authorization approval by the Ministry.

Arcturus COO Padmanabh “Pad” Chivukula and CEO Joseph E. Payne, Courtesy of Arcturus

“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. This represents a key milestone for the Company and provides significant clinical validation of our STARR™ platform. We believe self-amplifying mRNA combined with our LUNAR® delivery technology will create a path to better mRNA medicines,” said Joseph Payne, president and CEO of Arcturus.

ARCT-154 is also being evaluated in booster trials along with Arcturus’ other COVID-19 vaccine candidate, ARCT-165. In booster trials, which were administered at least five months after receiving the initial dose, ARCT-154 yielded robust 54-fold increases in neutralizing antibody responses against the Omicron variant.

Self-amplifying mRNA has been considered the next generation of RNA vaccines. By utilizing self-amplifying mRNA, vaccines can provide lower dose requirements because of sustained protein expression as the mRNA self-replicates. Lower dose requirements are useful for cost-effective manufacturing, and long-term efficacy and potency have recently highlighted problems with current mRNA vaccines targeting COVID-19, as pharma giants and regulators have speculated as to how many boosters are needed to have sufficient immunity.

Arcturus is also currently evaluating the technology in an influenza vaccine candidate, Lunar-Flu, and has several other mRNA therapeutics in the works for hepatic indications and cystic fibrosis.


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