Clinical-stage messenger RNA medicines firm Arcturus Therapeutics is set to initiate the Phase II clinical study of its vaccine candidate, ARCT-021, in the US.

ARCT-021 is an experimental vaccine that uses messenger RNA to inoculate against the coronavirus.

The development comes after Arcturus Therapeutics secured allowance of the investigational new drug (IND) application from the US Food and Drug Administration (FDA) after it reviewed data from the Phase I/II study.

Earlier, the Singapore Health Sciences Authority (HSA) approved the Phase II study of ARCT-021 in the country.

The Phase I/II study data showed favourable tolerability and both humoral and cellular immunogenicity on administering the drug.

Around 600 older and younger adult subjects will be enrolled in the Phase II study. ARCT-021 will be administered to 450 participants, while 150 individuals will receive a placebo.

Early interim safety and immunogenicity analyses will be conducted to select the dose for a Phase III study, which is slated to begin in the second quarter of this year.

Arcturus Therapeutics chief medical officer Steve Hughes said: “Allowance of the IND for our ARCT-021 Phase II clinical study represents an important milestone for the programme and we look forward to starting to screen study participants at US and Singapore clinical sites very soon.

“Our prior clinical results show that ARCT-021 administration results in humoral and cellular immunogenicity, and we are encouraged by an increasing body of evidence highlighting the potential importance of T cells in providing protection against SARS-CoV-2 infection and Covid-19.

“We believe that ARCT-021 holds promise to be a highly effective vaccine with a differentiated clinical profile, including the potential to only require a single dose for protection.”

In August last year, Arcturus Therapeutics dosed the first group of participants in the Phase I/II clinical study of its Covid-19 vaccine candidate.