Sure, 2020 will forever be known as the year of the COVID-19 pandemic. But 2021 just might be memorialized as the year the pandemic was defeated. Two COVID-19 vaccines have already received emergency use authorization (EUA) in the U.S. with a third vaccine also authorized in the U.K.

The big stories in the new year, though, could come from vaccines that haven't made it to market yet. It's possible that the stocks of the companies developing these experimental vaccines will deliver tremendous gains over the next 12 months. Here are three coronavirus stocks that are especially poised to soar in 2021.

Vaccine vials and a syringe next to stacks of cash

Image source: Getty Images.

1. Novavax

Novavax (NASDAQ:NVAX) ranked as the top-performing coronavirus stock of 2020 with a staggering gain of close to 3,000%. Can the biotech stock deliver another sizzling performance this year? Don't be surprised if it happens.

The company expects to report results from a late-stage study of COVID-19 vaccine candidate NVX-CoV2373 conducted in the U.K. in early 2021. Novavax initiated another late-stage study in the U.S. and Mexico last week. Look for results from this study sometime in the second quarter. 

If all goes well with these studies, billions of dollars will pour into Novavax's coffers. The company has deals in place with several countries (including the U.S., U.K., Australia, Canada, and New Zealand) to supply close to 300 million doses of NVX-CoV2373. 

This cash influx will help Novavax further explore the development of a COVID-19/flu combo vaccine. The biotech already has a promising flu vaccine candidate called NanoFlu that's on track for regulatory submissions. 

2. Vaxart

Vaxart (NASDAQ:VXRT) trailed behind only Novavax to become the No. 2 coronavirus stock of last year. It generated a sizzling return of around 1,600%. At one point in 2020, Vaxart's shares were up more than 4,700% year to date. I think the stock could have a lot more room to run in 2021.

The company is currently evaluating its COVID-19 vaccine candidate VXA-CoV2-1 in a phase 1 clinical study. Results from the study are expected this month. Vaxart hopes to quickly advance its experimental vaccine into phase 2 testing if the phase 1 results are positive.

VXA-CoV2-1 stands out from the leading coronavirus vaccines. It's a single-dose tablet instead of an injection. That makes Vaxart's vaccine more convenient to take and to distribute and store. The experimental vaccine also appears to promote mucosal immunity (immune system responses that occur in mucosal membranes in the eyes, nose, and elsewhere). 

Despite its impressive performance last year, Vaxart's market cap remains below $700 million. With the advantages offered by VXA-CoV2-1, the biotech will be worth a lot more than that if its clinical studies of the COVID-19 vaccine candidate go well.

3. Altimmune

Altimmune (NASDAQ:ALT) finished 2020 with its shares up close to 500%. By late July, the stock has soared more than 1,600% year to date. It's possible that Altimmune could regain those highs this year.

The biotech's COVID-19 vaccine candidate AdCOVID shares several things in common with Vaxart's experimental vaccine. It only requires a single dose. It can be stored at room temperature for extended periods. And it appears to provide mucosal immunity. The major twist is that AdCOVID is an intranasal vaccine.

There's one glaring problem for Altimmune right now, though. The U.S. Food and Drug Administration (FDA) placed a clinical hold on a planned early stage clinical study of AdCOVID because it wants changes to the study's protocols and additional manufacturing data.

I suspect that Altimmune will be able to quickly address the FDA's concerns and move forward with its study of AdCOVID. The company even stated that it doesn't expect the clinical hold will significantly change its overall timeline for the development of the vaccine. If AdCOVID delivers on its potential, Altimmune could be an under-the-radar COVID vaccine stock that skyrockets in 2021.

Remember the risks

Keep in mind that all three of these stocks are very risky. While their experimental COVID-19 vaccines look promising right now, there's always a chance that they'll disappoint in clinical testing. Novavax, Vaxart, and Altimmune are poised to soar in 2021, but they could easily sink instead. 

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.