COVID-19 dominated the news in 2020. It's not surprising, therefore, that the stocks of many companies fighting the coronavirus outbreak delivered stellar performances. 

As you might expect, the stocks of small companies generated much higher returns than those of big companies. But there were also significant differences in gains among smaller players. Which stocks ranked at the top? Here are the three best coronavirus stocks of 2020.

Gold dollar sign with coronavirus virions.

Image source: Getty Images.

1. Novavax

Novavax (NASDAQ:NVAX) blew away all other coronavirus stocks in 2020 with a sizzling gain of close to 2,850%. An initial investment of $10,000 in the biotech stock at the beginning of the year would have grown into nearly $300,000.

Investors cheered Novavax's results from a late-stage study of flu vaccine candidate NanoFlu early in the year. NanoFlu beat market-leading flu vaccine FluZone Quadrivalent in a head-to-head comparison. Novavax plans to file for U.S. Food and Drug Administration (FDA) approval for NanoFlu once it completes a manufacturing lot consistency trial.

However, Novavax's COVID-19 vaccine candidate NVX-CoV2373 clearly served as the biggest growth driver for the stock in 2020. The company recently initiated a late-stage study of the experimental coronavirus vaccine in the U.S. and Mexico. A U.K. late-stage trial of NVX-CoV2373 is already underway. Novavax expects to report results from this study in early 2021. 

The new year could be a happy one for Novavax shareholders. Novavax has major supply deals for NVX-CoV2373 with several countries, including the U.S., U.K., Canada, and Australia. If its COVID-19 vaccine wins approvals and emergency use authorizations, the biotech will soon have its first blockbuster product on the market.

2. Vaxart

Another COVID-19 vaccine maker also delivered tremendous returns in 2020. Shares of Vaxart (NASDAQ:VXRT) skyrocketed nearly 1,600% higher this year. At one point in July, the biotech stock was up more than 4,700%.

All this excitement centered on Vaxart's investigational coronavirus vaccine VXA-CoV2-1. The company reported encouraging preclinical data for the vaccine candidate earlier this year. 

VXA-CoV2-1 stands out in the coronavirus vaccine race for a couple of reasons. It's a tablet instead of an injection. This makes the vaccine more convenient to take and more easily distributed and stored than other leading COVID-19 vaccines. In addition, VXA-CoV2-1 requires only a single dose -- which could give it a cost advantage over other vaccines. 

Vaxart is currently evaluating VXA-CoV2-1 in a phase 1 study. It's too early to know how VXA-CoV2-1 will compare with the high efficacy levels of Pfizer's and Moderna's COVID-19 vaccines. However, if Vaxart's tablet vaccine proves to be safe and effective, it could be a big winner in the global market. 

3. Co-Diagnostics

Not all of the top-performing coronavirus stocks in 2020 belonged to vaccine makers. Co-Diagnostics' (NASDAQ:CODX) COVID-19 tests helped propel its shares to a gain of more than 1,900% this year.

The molecular diagnostics company quickly emerged as a leader in developing COVID-19 tests. By Jan. 31, Co-Diagnostics' novel coronavirus assay had successfully passed initial verification. Less than a week later, the company launched its first COVID-19 test. 

With COVID-19 cases soaring throughout much of the year, Co-Diagnostics' shipments of its tests soared. The company announced on Dec. 14 that it had sold more than 10 million of its Logix Smart COVID-19 test kits globally. 

As coronavirus vaccines become more widely available, the pandemic could draw to a close. That will likely taper Co-Diagnostics' dizzying growth. However, new mutations with the virus could mean that there will be a solid recurring demand for COVID-19 tests. The winning ways of this high-flying coronavirus stock just might continue into 2021 and beyond.

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.