Thanks to Moderna and Pfizer paving the way with their mRNA-based coronavirus vaccines, the market for mRNA medicines is finally open for business. But if you're looking to invest in the nascent companies making the therapies of the future, you might be in a bit of a pickle. There simply aren't that many mRNA stocks that are backed by a proven business. 

When it comes to more speculative investments, however, there are plenty of stocks to choose from. If investors play their cards right, they just might hit it big with a purchase of a smaller company angling to enter the space. But these contenders will be facing stiff competition from the heavyweights, and their success is far from guaranteed. Let's evaluate three mRNA drug developers to see what kind of upside investors can expect.

Vials of coronavirus vaccine and syringe next to hundred dollar bill.

Image source: Getty Images.

1. CureVac

The German biotech CureVac (NASDAQ:CVAC) has already rewarded shareholders this year, and it hasn't even had its first quarter of revenue from product sales yet. CureVac's most advanced program is its COVID-19 vaccine, which is currently in phase 3 clinical trials. Aside from that, it also has a rabies vaccine and a pair of cancer immunotherapies in phase 1.

Given that its coronavirus vaccine will need to compete with a plethora of other products if it's approved, it isn't reasonable for investors to expect the company to become a 10-bagger if they buy its stock right now.

But it could still deliver substantial growth with its second-generation mRNA vaccine in development. If CureVac's candidate can protect against multiple variants with one shot, as its creators intend, it'll have a distinct advantage over the existing options, which may require booster jabs to be fully protective. Still, the company's development collaboration with GlaxoSmithKline will limit its revenue potential to whatever it can earn in Germany, Austria, and Switzerland, so it probably isn't a millionaire-maker.

2. Arcturus Therapeutics

Like CureVac, Arcturus Therapeutics (NASDAQ:ARCT) is working to make an mRNA-based coronavirus vaccine. Its candidate, LUNAR-COV19, is still in phase 2 clinical trials, though it could get emergency approval by the end of this year if things go as planned. That puts it further behind the curve than CureVac. Nonetheless, its vaccine has a few logistical advantages that could come in handy if it's approved, like permissive storage requirements and a very low dose volume.

In terms of its other projects, Arcturus only has one clinical-stage program, its phase 1b therapy for ornithine transcarbamylase deficiency. If you've never heard of that disease, don't be too surprised; the company estimates that it affects only around 10,000 people globally. Simply put, Arcturus is a long way from commercialization, and it's targeting a very small niche, which might not be profitable without regulatory allowances like an orphan drug designation.

Even if its COVID vaccine pulls through, the fact is that it'll be fighting against entrenched competition that's had ample time to prepare. Early investors may have struck it rich with this stock if they sold in time, but for now, it doesn't look like people who buy it today are going to be rewarded.

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3. BioNTech

Per its coronavirus vaccine collaboration with Pfizer, BioNTech (NASDAQ:BNTX) is the only company on this list that's currently earning revenue as a result of its sales of mRNA medicines. It also has the largest and most developed pipeline of the bunch.

What's more, even if Pfizer decides to go its own way with future iterations of the coronavirus vaccine, BioNTech has gained a tremendous amount of technical know-how and public stature as a result of their collaboration. All of the above are positive signs for the company's future, even if they aren't necessarily a ticket to vast riches for investors.

It's hard to see how BioNTech could fail to capitalize on its current momentum. Management already has plans in place to reinvest earnings from the coronavirus vaccine, and the company has plans to diversify beyond its mRNA roots to cast a wider net. In the meantime, its phase 2 program for metastatic melanoma is highly promising, and it has a bevy of mRNA programs in phase 1 trials for other oncology applications. Over the course of this year, it'll start three new phase 2 trials, provide updates on five trials in progress, and initiate six first-in-human phase 1 trials.

Though none of these events have a realistic chance of making the stock double or triple overnight, they probably will provide a decent series of boosts that will please investors. But BioNTech's shareholders are probably already quite happy. In its latest earnings report, the company's quarterly revenue grew by more than 1,134% year over year, commanding a total of $482.32 million in trailing-12-month sales. If management can keep vaccine sales humming like that until its other pipeline projects are ready to hit the market, this stock will be a winner for years.

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.