What happened

Shares of Novavax (NASDAQ:NVAX) fell by an eye-catching 17.7% in September, according to data provided by S&P Global Market Intelligence. The vaccine specialist's shares have been locked into a multi-month downward trend of late for a variety of reasons. 

Chief among those reasons, Novavax has yet to earn an Emergency Use Authorization (EUA) in the U.S. for its COVID-19 vaccine candidate, NVX-CoV2373 -- a hurdle it originally expected to have cleared in May. The biotech now says it plans to file for an EUA with the Food and Drug Administration by the end of the year.

Meanwhile, Pfizer (NYSE:PFE), BioNTech, and Moderna have been racking up tens of billions of dollars in sales for their respective COVID-19 vaccines this year. Novavax, in short, is missing out on the party. 

A patient getting a vaccine in a clinic.

Image source: Getty Images.

So what

Another major problem facing the company is that several pandemic experts, and even some top biopharma companies like Pfizer and Roche, have started to suggest that the acute phase of the pandemic could be over within the next 12 months. Novavax's experimental COVID-19 vaccine, therefore, may have a shorter-than-expected commercial shelf life.

Now, Novavax's vaccine is still likely to do fairly well, sales-wise, internationally in markets such as India, Indonesia, and the Philippines past 2022. But there's no way to tell how it will fare in markets like Canada and the United States, where options are more abundant, once the acute phase of the pandemic comes to an end.

Complicating matters further, Atea Pharmaceuticals, Merck, Pfizer, and others may all apply for regulatory approval for their oral COVID-19 antiviral treatments within the next six months. These easy-to-use pills may be taken by patients at home in some cases, and effective treatments for the coronavirus might further erode the demand for COVID-19 vaccines.   

Now what

Is Novavax's stock worth buying on this prolonged slide? Over the past 90 days, the biotech's shares have fallen by more than 22%. That's not surprising with Pfizer and Moderna dominating the vaccine market in the U.S. and Merck's oral COVID-19 medication showing promise in late-stage trials. Novavax's main share-price driver over the past year, after all, has been the commercial promise of NVX-CoV2373. 

Novavax's stock could certainly rebound. There's no guarantee that these oral medications will turn out to be safe enough to use in a home setting, and there remains the possibility that new variants might require another global vaccination effort. All that being said, there are scores of other biotech stocks that arguably sport more compelling risk-to-reward ratios than Novavax's right now. 

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.