It was the moment we all were waiting for. The U.S. Food and Drug Administration (FDA) granted Novavax's (NVAX 4.21%) coronavirus vaccine Emergency Use Authorization (EUA) last week. Originally, Novavax had hoped to win access to the U.S. market last year. But manufacturing struggles delayed its regulatory request by several months.

Meanwhile, Novavax has gained authorization in nearly 40 other countries over the past several months -- and started to generate revenue and profit from its vaccine. So, we might have expected the shares to climb following the nod from the U.S. Instead, they lost 26% in one trading session. Now, Novavax shares are down about 60% year to date. Does this mean it's time to give up on Novavax? Let's take a closer look.

Reasons behind the decline

There may be a few reasons behind Novavax's one-day drop. First, there's a bit of "buy the rumor, sell the news" going on. The stock actually climbed 22% from the first day of July until Novavax announced its product authorization on July 13.

The company already won a nod from an FDA advisory committee in June. The FDA doesn't have to follow the advisory committee's recommendation. But it usually does. So, investors clearly bet on Novavax winning here. And then some decided to lock in gains.

A bit of concern about Novavax's safety profile also may have hurt the shares last week. The European Medicines Agency added severe allergies as a possible side effect to watch for after vaccination. I wouldn't expect this to weigh on the shares for long though. Today's leading vaccines -- those of Pfizer and Moderna -- have had similar troubles.

Health authorities noted rare cases of heart inflammation following administration of the Pfizer and Moderna vaccines in teens and young men. These issues haven't hurt vaccine demand -- or share prices.

And, finally, Novavax's declines may also be due to a shift in investing trends. Investors aren't as excited about vaccine stocks as they were a year ago. This means there wasn't a rush to get in on Novavax after the EUA.

What's next for Novavax

All of this explains the recent share movement. Now let's have a look at what's next for Novavax.

The company already has shipped vaccine from its manufacturing site at the Serum Institute of India to the U.S. It's now waiting for vaccination policy recommendations from the Centers for Disease Control and Prevention. A CDC advisory committee will review the vaccine during a meeting tomorrow. After the CDC issues guidelines, vaccine rollout can begin.

The U.S. recently ordered 3.2 million doses of the Novavax vaccine. This isn't a huge number of doses. But it's not a surprise. About 67% of the U.S. population is fully vaccinated. So the opportunity in the U.S. today is limited.

Now, let's talk about whether you should give up on Novavax. The biotech company has predicted revenue of $4 billion to $5 billion this year. This is great news considering the company didn't have product revenue a year ago. The vaccine is Novavax's first commercialized product. Still, it's very far from the $32 billion in coronavirus vaccine revenue that Pfizer expects to generate this year.

It's also important to look at what may be down the road for Novavax. The company is farthest ahead in a race to develop a combined coronavirus/flu vaccine. Its candidate is set to enter phase 2 trials this year. Moderna also is working on a combined vaccine -- but its candidate is in preclinical studies. A combined candidate could be a leader in the coronavirus market of the future. It's an easy option that may attract the population that usually goes for a flu shot.

A future winner?

Novavax may not be a market leader now. But it could be in the future.

All of this means the shares may take a while to advance. As I mentioned above, vaccine stocks aren't as popular as they were earlier in the pandemic. And Novavax will need some time to show its coronavirus vaccine can drive revenue over the long term.

What's an investor to do? I don't think now is the time to give up on this biotech stock. I'm still optimistic about Novavax. Today, it's better off than it was a year ago. It's generating product revenue and profit. It's carving out a spot in the market. And in the future, it may release a product with market-leading potential.

That said, Novavax doesn't belong in every portfolio. It remains a risky stock. Novavax's share of the market may remain small. And it's too early to say whether Novavax -- and rivals -- will be able to bring a combined vaccine to market. Investors who are uncomfortable with these risks may not want to stick around.

But investors with tolerance for risk -- and the patience to wait a few years -- might want to hold onto this vaccine player. If Novavax maintains a share of the vaccine market and eventually succeeds with a combination product, rewards down the road may be big.