Shares of Moderna (MRNA 0.42%), Inovio (INO -2.58%), Novavax (INO -2.58%), and other companies in the race to develop a coronavirus vaccine have skyrocketed over the past several months, with investors betting on which company will reach the finish line first. So far this year, Moderna and Inovio have surged by 297% and 528%, respectively -- and Novavax is up by more than 36-fold.

A researcher holds a syringe filled with vaccine.

Image source: Getty Images.

As the coronavirus pandemic deepened, the U.S. government put forth a plan to help accelerate vaccine development. Through Operation Warp Speed, the government has granted a total of billions of dollars to various companies, with the goal of bringing a vaccine to market by January.

At the same time, companies have been pushing their vaccine candidates into human trials at record speed. Moderna, for example, launched a phase 1 trial in March, and this week the drug entered phase 3 -- the final step before regulatory approval. Most leaders in this race have published favorable phase 1 data by now, and some have moved into stage 3 studies. AstraZeneca (NYSE:AZN) and the team of Pfizer (NYSE:PFE) -- BioNTech (NASDAQ:BNTX) have done both. 

Should I sell?

If you bought shares of one of these players months ago, you have reason to celebrate. But you also may be starting to ask yourself this question: Considering the enormous gains, should I sell?

The answer to this depends on your investment style and risk appetite. And it's important to look at each company individually rather than buying or selling a basket of vaccine makers as a whole.

Some of these businesses are still at the clinical stage, meaning they're a few years away from possibly commercializing a product (besides the potential coronavirus vaccine). That's the case for Moderna and Inovio. A commercialized coronavirus vaccine for these companies would be a double win: It would give them a marketed product and highlight the efficacy of their technologies. On the other hand, a failure for any of their coronavirus trials would be a big loss, because the companies don't have another product to drive revenue in the near term.

Then there are the big pharma players, including AstraZeneca and Pfizer. AstraZeneca has partnered with the University of Oxford, and Pfizer is collaborating with biotech company BioNTech on vaccines.

These companies have vast portfolios of marketed products and future medicines in the pipeline. Their futures don't depend on the coronavirus vaccine. In fact, though AstraZeneca is one of the leaders in the race, its shares have only gained 13% this year, and Pfizer shares are down 1.2%. These stocks are less reactive to coronavirus vaccine news. That means a vaccine failure may not crush them, but also that a victory may not produce the gains we've seen in biotech stocks.

Different from the rest

And finally, there is Novavax. This company is in a unique position: It's a clinical-stage biotech -- but maybe not for long. Novavax recently reported solid results from a pivotal trial on its flu vaccine, NanoFlu, and plans to apply for regulatory approval. Like its fellow clinical-stage companies Moderna and Inovio, Novavax's shares have surged. But it has the advantage of a possible product close to market if the coronavirus vaccine program fails. That said, the company may still be overvalued after recent gains.

What's your style?

If you're at the start of your investing days and have a strong appetite for risk, you might consider holding shares of the clinical-stage companies whose late-stage trials have just begun; further positive data or progress may drive them even higher. Still, keep in mind that any setbacks for the companies at this point -- or a clear win for a rival -- could weigh heavily on these shares. As I always say, anything can happen during a clinical trial. And that's why investors with a lower appetite for risk should be particularly cautious at this stage -- you might even even consider reducing your position.

The big pharma companies may represent an exception. As mentioned above, the size of their product portfolios means the coronavirus vaccine is less likely to drive share gains (or losses).

Whatever you decide, what is crucial for investors right now is to closely watch clinical-trial news. The strength of the data will determine which stocks will continue to climb and which will fall behind.