Arcturus Therapeutics (NASDAQ:ARCT) soared 299% in 2020 as it advanced its coronavirus vaccine candidate into human trials. Investors were betting that the investigational mRNA vaccine would demonstrate efficacy to rival similar ones developed by bigger rivals Pfizer (NYSE:PFE) and Moderna (NASDAQ:MRNA).

Now the question is whether you missed out on your chance to profit from Arcturus' potential if you didn't invest early last year -- or if there could be more big share price gains to come.

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Arcturus has been aiming to produce a vaccine that would be effective in a one-dose regimen -- as opposed to the Pfizer and Moderna vaccines, which require two doses.  That's one of the reasons why shares of the company have been soaring. If Arcturus develops a safe, effective COVID-19 vaccine that works without a booster shot, it could eventually take market share from rivals.

But here's the problem. Arcturus recently disappointed investors with a data report from its phase 1 trial. In that one-dose regimen, its candidate produced neutralizing antibodies at lower levels than the Pfizer and Moderna's vaccines. That's key, because those neutralizing antibodies are what bind to the coronavirus and prevent it from infecting human cells.

Still, Arcturus said the vaccine candidate produced immune responses in all trial participants and was well-tolerated. The company now is launching a phase 2 trial that will study both one-dose and two-dose regimens in 600 volunteers.

Arcturus' chances of developing a one-dose vaccine that meets or surpasses the efficacy of the Pfizer and Moderna vaccines appear slim. But it's continuing to explore the option. And Arcturus still holds another advantage. Its vaccine candidate is freeze-dried, which makes transportation and storage easy. By comparison, the ultra-low temperature requirements for Pfizer's vaccine make its distribution unusually challenging.

If Arcturus delivers even a two-dose vaccine as efficacious as those of its rivals, it could take some market share due to that factor. So any positive news from the phase 2 trial is likely to lift shares of the biotech company. But unless Arcturus surprises us with stronger-than-expected one-dose data, I wouldn't expect a triple-digit share gain in 2021.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.