If you had bought Novavax (NVAX 7.87%) stock at the beginning of the year, you would be a happy investor right now. Shares of this biotech company have skyrocketed by almost 2,000% year to date, a rare feat even within the volatile biotech industry. Novavax has been able to achieve these returns thanks to its involvement in the hunt for a vaccine for COVID-19.

It's natural to wonder whether now is a good time to cash in on Novavax; after all, no one can argue with gains like that%. However, if Novavax continues to climb, it might make more sense to hold on to its shares, even after its dazzling run since the beginning of the year. With that in mind, here are three things that could cause Novavax's stock to jump even higher.

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1. Regulatory filing for the company's potential flu vaccine

Back in March, Novavax reported positive results from a phase 3 clinical trial for NanoFlu, a potential flu vaccine the company is developing for adults aged 65 and older. The trial pitted Novavax's NanoFlu against Fluozone, which is currently one of the leading such vaccines on the market and is marketed by Sanofi. The primary endpoint of the trial was to "demonstrate non-inferior immunogenicity of NanoFlu" when compared to Fluzone. The trial also compared NanoFlu's safety profile with that of Fluzone. During the trial, NanoFlu achieved its primary endpoint. And with these positive results in its back pocket, Novavax is now gearing up to submit a Biologics License Application (BLA) for its potential flu vaccine. 

Importantly, NanoFlu was granted a fast-track designation by the U.S. Food and Drug Administration (FDA). This designation is reserved for drugs (or vaccines) aimed at serious conditions for which there is an unmet medical need. This nod of approval from the health industry regulator means this vaccine is likely to go on to earn regulatory approval and become highly lucrative. Once Novavax officially announces the filing of a BLA for NanoFlu, it could invite more investors to purchase its shares and send its stock even higher. 

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2. Positive results from this clinical trial

In late May, Novavax initiated a phase 1/2 clinical trial for its investigational COVID-19 vaccine, NVX-CoV2373. The trial will be held in two phases. The first of these will be conducted in Australia and will enroll 130 healthy participants aged 18 to 59, each of whom will receive two doses of the vaccine. This phase of the trial will test the vaccine's safety and immunogenicity.

The second phase of the study will be conducted in several countries, including the U.S., and will test NVX-CoV2373's safety, immunity, and disease reduction in a broader age range of participants. Novavax said it expects preliminary safety and immunogenicity data from this trial in July. When these results come in, the company's stock could soar -- if, of course, the results happen to be to investors' liking. 

3. Could Novavax join Operation Warp Speed?

The U.S. government recently launched Operation Warp Speed, an initiative meant to accelerate the development of a vaccine for COVID-19. Five pharmaceutical and biotech companies were initially selected as part of this operation: Merck, Johnson & Johnson, AstraZeneca, Moderna, and Pfizer. However, the government has since enrolled other companies for this operation. For instance, Emergent BioSolutions landed a task order, valued at $628 million, for the production of several government-backed coronavirus vaccine candidates.

Also, Vaxart was selected to take part in the government's nonhuman primate (NHP) challenge study, which will test the effectiveness of several COVID-19 vaccine candidates. While Novavax is still sitting on the sidelines of this particular initiative, the company could eventually be enrolled in the operation. And if it earns that high honor, its stock could jump sharply, which is what happened to Vaxart's stock when it announced it would take part in Operation Warp Speed. 

Novavax remains risky

While these catalysts could send Novavax to new heights, lots of things could cause the company's stock to fall off a cliff -- for instance, negative results from the aforementioned clinical trial, or another company coming close to launching a vaccine for COVID-19 on the market before Novavax. In short, I think Novavax remains a risky stock to invest in, but for those willing to take the risk, I believe this biotech stock is worth considering.