You'd no doubt be quite pleased if some of the stocks in your investment portfolio had doubled year to date. A return of 100% or more in half a year would certainly be something to smile about.

But what if you owned a stock that delivered a gain of almost 2,000% in the last six months? That's the kind of performance that would warrant much more than just a smile. Perhaps cartwheels would be in order.

There's at least one stock that has actually generated such a sizzling year-to-date return: Vaxart (NASDAQ:VXRT). But is it too late to buy this high-flying biotech stock?

Dollar sign casting a shadow shaped liked a question mark

Image source: Getty Images.

Behind Vaxart's huge gains

Investors were excited about Vaxart's prospects coming into 2020. The biotech focuses on developing oral vaccines. Its pipeline candidates included oral tablet vaccines for protecting against norovirus, influenza, and respiratory syncytial virus (RSV).

Then came the COVID-19 outbreak. On Jan. 31, Vaxart announced that it planned to develop an oral vaccine for the novel coronavirus. Its share price had already more than doubled before the news, but skyrocketed even more, as investors were eager to jump aboard any company with a promising COVID-19 program.

On Feb. 27, Vaxart announced plans to sell 4 million shares at a price of $2.50 per share. The fantastic part of the story was that the stock had been trading at only $1.65 at the previous day's close. As you might imagine, Vaxart's shares soared yet again.

The next big catalyst for Vaxart came on April 21, with the company's positive preclinical testing results for its oral COVID-19 vaccine. In subsequent weeks, though, the stock gave up some of its gains. The pause didn't last long: Vaxart joined the Russell 3000 index on June 24, providing another big catalyst.

But the biggest news of all for Vaxart was only a couple of days away. On June 26, the biotech announced that its oral COVID-19 vaccine had been selected for funding by the U.S. government's Operation Warp Speed.

Reasons it could go higher

Could Vaxart stock keep its incredible momentum going? It's possible.

The company plans to begin a phase 1 study of its oral COVID-19 vaccine in the second half of the year. CEO Wouter Latour has indicated this study could crank up as early as this summer.

Despite its meteoric rise, Vaxart's market cap is still only around $620 million. You can count on that number rising tremendously if the biotech's COVID-19 vaccine proves to be successful in its phase 1 clinical trial. If the vaccine candidate makes its way unscathed through three phases of clinical studies, Vaxart stock will be worth a lot more than it is now.

Don't forget Vaxart's other pipeline candidates. The biotech reported positive results earlier this year from a phase 2 study of its oral tablet influenza vaccine in immunization against one flu strain. If the vaccine is proven in subsequent studies to be effective against a quadrivalent mix of flu strains, Vaxart could have a winner on its hands.

Johnson & Johnson is collaborating with Vaxart on a universal oral flu vaccine. This vaccine is only in preclinical testing right now, but results from these tests should be on the way this summer. Vaxart also reported positive results from a phase 1 study of its oral norovirus vaccine. The company, however, has put the program on hold while it looks for a partner for advancing the development of that vaccine.

Huge potential, huge risks

There's a huge potential for oral vaccines for COVID-19, influenza, and other viruses. It's not hard to envision Vaxart's share price tripling, and perhaps generating much higher returns than that, over the next couple of years -- if all goes well with its clinical testing.

That's a big if for now, though. Just as Vaxart's potential is huge, so are its risks. Only around 16% of vaccines in phase 1 testing go on to win approval from the Food and Drug Administration. And Vaxart's COVID-19 vaccine still hasn't entered phase 1 yet.

It's not too late to buy Vaxart, in my view. However, I think that for most investors, it's still too early to buy the stock.