With shares of Moderna (NASDAQ:MRNA) up around 330% year to date, investors have to be asking themselves, "Is Moderna still worth holding?"

The jump in value, from a market cap of $6.6 billion at the beginning of this year to $23.4 billion, is due to the potential for mRNA-1273, Moderna's vaccine to prevent COVID-19. The company has only released a little data from the phase 1 clinical trial, but the phase 2 study is already underway, and the biotech plans to start a phase 3 clinical trial next month.

As the maker of the most advanced U.S.-based vaccine, Moderna certainly deserves a premium over other early stage biotechs developing COVID-19 vaccines, such as Inovio (NASDAQ:INO) and Novavax (NASDAQ:NVAX). But it's debatable whether the potential for mRNA-1273 is worthy of a $16.8 billion increase in Moderna's valuation when Inovio's entire market cap including its pipeline is only $3.3 billion, and Novavax, which has an influenza vaccine that's reported positive phase 3 results, is only worth $4.1 billion.

Hands about to inject into a shoulder

Image source: Getty Images.

Whether Moderna is still worth holding at this lofty valuation depends largely on how quickly its competitors can get to market with their COVID-19 vaccines and take market share away from Moderna. Of course, mRNA-1273 also has to be successful to justify holding, but anyone who is buying at this valuation must assume that success is virtually guaranteed, given that Moderna's pipeline of its other drugs was only worth $6.6 billion before the pandemic started.

That's a long way to fall if mRNA-1273 fails to live up to the hype.

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.