What happened

Shares of Arcturus Therapeutics Holdings (NASDAQ:ARCT) were soaring 12.7% higher as of 3:28 p.m. EST on Tuesday. The big jump came after the clinical-stage biotech provided its third-quarter update following the market close on Monday. Investors were less interested in Arcturus' financial results than they were in the company's encouraging interim phase 1/2 results for its coronavirus vaccine candidate ARCT-021.

So what

There's no question that ARCT-021 looked promising based on the company's interim phase 1/2 results. What's especially attractive is that it could be effective at low doses.

Gloved hands holding syringe and vaccine bottle

Image source: Getty Images.

Investors' excitement about Arcturus' third-quarter update comes hot on the heels of Pfizer and BioNTech reporting efficacy of 90% or greater for their experimental coronavirus vaccine BNT162b2 on Monday. Both ARCT-021 and BNT162b2 use messenger RNA (mRNA). The apparent success for BNT162b2 could bode well for Arcturus' COVID-19 vaccine candidate.

It's important not to get too carried away just yet, though. Arcturus hasn't advanced ARCT-021 to late-stage clinical testing yet. There are several key hurdles to jump before we know if the experimental vaccine is safe and effective. Also, just because another mRNA-based vaccine achieved impressive results doesn't guarantee that ARCT-021 will follow suit.

Now what

Arcturus plans to talk with regulatory authorities in Singapore this week about its design for a late-stage study of ARCT-021. The company also stated that it will engage with the U.S. Food and Drug Administration about advancing the experimental vaccine to late-stage testing "very shortly." With the promising early results for ARCT-021, the biotech stock appears to be one for aggressive investors to keep on their radars.