What happened Shares of Arcturus Therapeutics (NASDAQ: ARCT) were soaring 34.7% higher as of 10:56 a.m. EDT on Tuesday. The big jump came after the company announced that Singapore regulators approved the advancement of two messenger RNA COVID-19 vaccine candidates into phase 1/2 clinical testing. So what The Singapore Health Sciences Authority gave the green light for Arcturus to initiate a phase 1/2 clinical trial featuring mRNA vaccine candidates ARCT-154 and ARCT-165. This study will evaluate these candidates as primary vaccines and as boosters following initial vaccination with Comirnaty, the COVID-19 vaccine developed by Pfizer and BioNTech. Image source: Getty Images. Singapore's decision came on the heels of another win for Arcturus. The company announced on Monday that the Vietnamese government approved advancing ARCT-154 into a phase 1/2/3 clinical study. There's even more good news for Arcturus. The Singapore clinical study is being partially funded by a grant that the country's government already awarded to the clinical-stage biotech company. Arcturus' manufacturing partner, Vinbiocare, is funding the clinical trials in Vietnam. It's understandable why these stories provided solid catalysts for the biotech stock. However, investors should keep in mind that Arcturus still has several big hurdles to jump over before either of its two mRNA vaccine candidates will have a chance at winning regulatory approvals. Now what Arcturus plans to kick off its Singapore clinical study within the next few weeks. The company could have more news on its pipeline progress when it provides a second-quarter update on Aug. 9. 10 stocks we like better than Arcturus Therapeutics Holdings Inc.When our award-winning analyst team has 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.* They 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 June 7, 2021 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