Who wants to be a millionaire? The answer to the question is obvious: Nearly everyone.

Going on a TV game show is one path to becoming a millionaire. However, many more people have become successful through investing in stocks than have done so through Who Wants to Be a Millionaire. The stocks most likely to line your pockets are those that you buy when they're small and not as well known. These stocks will also have a massive potential market and a product or service that gives them a big advantage in that market.

One stock that meets these criteria is Altimmune (ALT 2.87%). Could this under-the-radar COVID vaccine stock be a millionaire-maker?

Yellow sticky note with coronavirus drawn on it on top of a chalk drawing of a dollar sign

Image source: Getty Images.

The Altimmune alternative

Altimmune definitely checks off the small and relatively unknown boxes. The company's market cap stands below $400 million even after its stock soared close to 500% in 2020. Altimmune's search engine traffic barely registers compared to leading COVID-19 vaccine makers like Pfizer and Moderna

There's also no disputing that the potential market for coronavirus vaccines is massive. Bernstein analyst Ronny Gal estimates the COVID-19 vaccine market this year will approach $40 billion. How big the market will be in the future hinges on how long the immunity provided by the vaccines lasts. It's possible that we could be looking at a similar-sized annual market going forward.

That leaves one hoop for Altimmune to jump to become a huge winner -- offer a product with a significant competitive advantage. The company thinks that it has this covered, too.

Altimmune's COVID-19 vaccine candidate AdCOVID addresses several drawbacks of the current vaccines on the market. It requires only a single dose, compared to two doses for Pfizer's and Moderna's coronavirus vaccines. AdCOVID is given intranasally, making it more convenient to administer than injected vaccines. It doesn't have any cold storage requirements. Even better, Altimmune's experimental vaccine appears to provide mucosal immunity, or immune responses that occur in mucosal membranes. This is an important advantage since the coronavirus initially infects the mucous membranes in the nose and mouth.

What it would take

It certainly seems that Altimmune fits the bill of the kind of stock that's most likely to be a millionaire-maker. But what would it take for Altimmune to actually make it happen?

First of all, we'll need to assume the size of the initial investment. If you invested $500,000 in Altimmune, the stock would only need to double to turn the initial amount into $1 million. However, most people don't have that kind of money to invest in one stock (and probably shouldn't do so even if they did). Let's instead assume an initial investment of $10,000. 

For Altimmune to turn $10,000 into $1 million, the stock would need to grow 100 times bigger. This means that Altimmune's market cap would have to expand from a little under $400 million today to close to $40 billion. 

Is it possible for Altimmune to make this jump? Sure it is. A $40 billion market cap is in the ballpark of Moderna's current size. Altimmune would need to have stellar clinical results for AdCOVID. The coronavirus vaccine would have to become a major commercial success. It would help if Altimmune's other pipeline candidates, including experimental intranasal flu vaccine NasoVax and chronic hepatitis B therapy HepTcell, were also proven both safe and effective.

A long way to the top

There is an entirely plausible path for Altimmune to become a millionaire-maker, but it isn't an easy one.

AdCOVID hasn't even advanced into clinical testing in humans yet. The U.S. Food and Drug Administration placed a clinical hold on Altimmune's application to begin phase 1 testing of the experimental vaccine. This shouldn't stop the show, though. The FDA has questions about manufacturing data for AdCOVID and wants Altimmune to modify some protocols of its planned clinical trial. Altimmune doesn't think the clinical hold will significantly affect its overall timeline for developing AdCOVID.

But even assuming the FDA's clinical hold is removed relatively soon, Altimmune faces multiple challenges to get AdCOVID to market. It's quite possible that the company's vaccine candidate won't meet investors' lofty expectations.

The hard rock group AC/DC once sang, "It's a long way to the top if you wanna rock and roll." That sentiment applies to biotech stocks, too. It's a long way to the top for Altimmune to become a millionaire-maker, but the small biotech has more of what it takes to make it to the top than many stocks do.