In an investor update on Monday, Arcturus Therapeutics Holdings (NASDAQ: ARCT) reported early-stage clinical trial results for its coronavirus vaccine candidate. The company also said that the Singapore Health Sciences Authority had granted approval to begin a phase 2 study of that candidate, ARCT-021. Although the results indicate that the one-dose vaccine is effective at blocking the coronavirus, it produces fewer neutralizing antibodies than the vaccine made by Pfizer (NYSE: PFE) and BioNTech (NASDAQ: BNTX), and the vaccine of Moderna (NASDAQ: MRNA). Compounding that, Pfizer/BioNTech's BNT-162b2 and Moderna's mRNA-1273 have been approved by U.S. and European Union healthcare regulators for emergency use. Like BNT-162b2 and mRNA-1273, Arcturus' vaccine candidate utilizes messenger RNA to instruct the body's cells how to combat the coronavirus. Image source: Getty Images. Still, in its press release disseminating the news, Arcturus emphasized the successes of ARCT-021 in the trials. "The Phase 1/2 study results, together with recently generated pre-clinical data, indicate that ARCT-021 leads to a potent immune response to SARS-CoV-2, and demonstrates a differentiated biological profile whereby the immune response increases in the weeks following vaccination," said Ooi Eng Eong, a member of its vaccine platform scientific advisory board, according to the company. The company expects to harvest phase 2 data early next year; it did not get more specific. Arcturus was considered by many to be an underdog in the race to bring a coronavirus vaccine to market. ARCT-021's results relative to its Pfizer/BioNTech and Moderna rivals are disappointing, and only exacerbate that status. As a result, the company's stock plummeted on Tuesday: down by nearly 55% on the day, far exceeding the modest decline of the S&P 500 index. 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 November 20, 2020 Eric Volkman has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source