Are you the kind of person who sees the glass as half-full or half-empty? The answer will probably determine how you look at Novavax (NVAX -7.42%).

The stock has delivered a return of more than 70% year to date. Many investors would think that's great. However, others would look at the opportunities Novavax has failed to capitalize on because of delays in filing with regulators for authorizations for its COVID-19 vaccine. Prior to when those setbacks began, the stock was up by nearly 190% for the year.

But is Novavax stock a buy now? Again, there are different ways to look at the question. Here are the bull and bear arguments for this vaccine stock.

A healthcare professional giving a shot to a patient.

Image source: Getty Images.

Bull case: A much better story now

Keith Speights: Novavax's disappointing filing delays are now water under the bridge. The company has not only completed most of its regulatory submissions for COVID-19 vaccine NVX-CoV2373, it has also already picked up several key wins.

Indonesia and the Philippines each issued an Emergency Use Authorization (EUA) for NVX-CoV2373 in November. Over the past several days, Novavax secured an Emergency Use Listing (EUL) from the World Health Organization and authorization from the European Union's regulator, too.

The latter two victories are especially important. That EUL was a prerequisite for Novavax and its partner, Serum Institute of India, to distribute NVX-CoV2373 to low- and middle-income countries that are part of the COVAX Facility. Novavax's European authorization paves the way for it to supply at least 100 million doses of its vaccine to the EU.

But there are plenty of other potential catalysts on the way. Novavax awaits regulatory decisions in multiple countries, including Australia, Canada, South Korea, and the U.K. And it should file for its U.S. EUA any day now.

Over the longer term, Novavax could be a winner with a combination COVID-19/flu vaccine. The company previously reported positive results from its late-stage study of flu vaccine candidate NanoFlu. It's now testing a combo of NanoFlu and NVX-COV2373. Based on all of this, the stock has a much better story now than it has over recent months.

Bear case: There are more attractive valuations in the vaccine space

Alex Carchidi: Even if it's a strong company that's going to make billions of dollars selling its coronavirus vaccine, Novavax's valuation is quite pricey in comparison to other vaccine stocks at the moment. Specifically, Moderna (MRNA -0.15%) and Pfizer (PFE 0.88%) trade at far more reasonable valuations, though both have been profitably selling their COVID-19 inoculations globally for many months.

Novavax's price-to-sales ratio is 11.18, considerably higher than Moderna's 9.53 or Pfizer's 4.8. That means new investors will be paying a moderate premium for each dollar of its revenue. Likewise, the enterprise-value-to-free-cash flow ratio of Moderna is 9.05, whereas Pfizer's is just over 12 -- but Novavax's is a sky-high 30.1. Here too, investors will be paying a vastly higher price per dollar of cash flow if they buy Novavax stock instead of Moderna's. Other common valuation metrics like price-to-book ratio paint a similar picture.

In addition, the market is already pricing in recent catalysts for Novavax, like when regulators from the World Health Organization and the EU on Dec. 20 signed off on NVX-CoV2373 for emergency use. When the market heavily expects a result like a vaccine approval and then that result occurs, it doesn't always boost shares further, as the expected future value of the company may be largely the same as it was before. And it's exactly these high expectations for its future earnings that may explain why Novavax's stock is still down by around 2.5% over the last month despite those positive developments.

In sum, Novavax's stock is a bit overvalued, and its upside may be more limited than shareholders hope. Plus, investors can find comparable growth prospects at better prices elsewhere.

Past vs. future

The bear argument for Novavax focuses more on the company's past. The valuation metrics referenced are all based on the previous 12 months. However, Carchidi could be right that the market is already pricing in the catalysts for the stock.

On the other hand, the bull case for Novavax is focused almost entirely on the future. It anticipates more regulatory wins for NVX-CoV2373 and positive developments for the company's combo COVID-19/flu vaccine. And the bull argument assumes that these victories will drive Novavax's share price significantly higher. There's no guarantee that will happen.

Is Novavax stock a buy? It depends on how much weight you give to the company's less-than-stellar past compared to the weight you're putting on its still-uncertain future.