The Maryland-based biotech firm’s vaccine has been touted by many as the next vaccine breakthrough that could potentially help efforts to vaccinate Americans who have been hesitant to receive other vaccine options.

That’s because the protein-based vaccine uses a technology that’s been around for decades, and has long been used in flu shots and vaccinations in babies against hepatitis-B. Familiarity with that older technology could result in many who have been hesitant to receive the mRNA vaccines from Pfizer and Moderna, although they have proven to be safe and effective.

In the U.S., the not-yet-released Novavax vaccine has accumulated a large number of fans, who have been posting on social media platforms like Reddit and Twitter for months that they have held off on getting a vaccine until Novavax’s becomes available.

But the longer the FDA approval takes, the more its stock continues to fall.

At the time of publication, Novavax was trading at $73.50, down from its most recent peak at $88.75 on March 1, and nearly half its overall 2022 peak at $142.90 on Jan. 3.

Novavax did not respond to Fortune’s request for comment. 

A slow FDA process

The FDA has not commented on the company’s pending application and there is no meeting scheduled with the FDA’s advisory committee, a necessary step towards authorization.

Experts say that until Novavax’s authorization in the U.S. gains traction, its stock price will likely continue to struggle.

“Every day that goes by that they don’t get an [advisory committee] meeting scheduled with the FDA is another day where it could take even longer to actually get approved,” Will Sevush, a healthcare equity strategist at Jefferies Group, an investment bank, told Fortune. “The longer it takes, the more their opportunity set is shrinking.”

Novavax’s application process with the FDA has taken longer compared to the other authorized vaccines from Pfizer/BioNTech, Moderna and Johnson & Johnson. Each had an advisory meeting scheduled within a month of submitting their application. It’s unclear why there has been more of a delay with Novavax. 

Some experts are calling on the FDA to move forward with the Novavax vaccine, which has already won approval in Australia, India, Europe and several other countries and regions since last November. 

“FDA must stop slow walking authorizing Novavax,” said Lawrence Gostin, director of the O’Neill Institute for National and Global Health Law at Georgetown University, in a tweet this week. “Every major regulatory agency has authorized it. It has good clinical data. A more traditional vaccine is easier to use & more acceptable to the public.”

Trouble in Europe?

On Monday,  news broke that Novavax’s rollout in Europe has been slow, and that its impact on unvaccinated populations may not be as significant as expected, Reuters reported.  

In Germany—which Reuters reported has more than 10 million unvaccinated adults—only about 38,000 Novavax doses have been administered since the start of the rollout on Feb. 24, according to data from the Robert Koch Institute, a German federal agency. Similarly small Novavax rates were reported in Italy and France.

Novavax representatives in the U.S. have said its vaccine will help encourage unvaccinated Americans to finally get vaccinated, even as the country moves towards treating COVID-19 as an endemic disease. In an interview with CNN late last year, Novavax CEO Stanley Erck said the “primary market” for his company’s vaccine was “people who have been hesitant to get other vaccines.”

And as recently as this week, representatives from the company referenced that same line of thinking. 

“What is so amazing to us is the number of people around the world who tell us that even though they have had other choices in vaccination, they are waiting for our vaccine,” said ​​Silvia Taylor, SVP of global corporate affairs in an interview with PR Week. 

Sevush told Fortune that the news out of Europe is likely contributing to the company’s struggles in the stock market. 

As of March 15, 76.7% of the U.S. population had received at least one dose of a coronavirus vaccine, while 65.3% were fully vaccinated, according to the Mayo Clinic’s vaccination tracker.