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. 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. 10 stocks we like better than Arcturus Therapeutics Holdings Inc.When investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Arcturus Therapeutics Holdings Inc. wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of October 20, 2020 Keith Speights owns shares of Pfizer. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source