Novavax (NVAX -0.76%) has given plenty of reasons for skeptics to doubt whether or not it would be successful. You can go back to the company's multiple flops in clinical trials of its experimental respiratory syncytial virus vaccine over the past few years. You can also point to Novavax's repeated delays in filing for regulatory approvals and authorizations of its COVID-19 vaccine candidate NVX-Cov2373.

However, Novavax announced its third-quarter results after the market closed on Thursday. I think that it's time to buy this vaccine stock after the biotech's Q3 update. Here are three reasons why.

A scientist holding a COVID-19 vaccine vial with one hand and giving a thumbs-up with the other hand.

Image source: Getty Images.

1. Regulatory filings are on track

Novavax's management team at long last were able to point to successes with regulatory filings. NVX-CoV2373 even recently won its first Emergency Use Authorization (EUA) in Indonesia. 

Over the past couple of weeks, Novavax completed regulatory submissions in the United Kingdom, Australia, Canada, European Union, India, New Zealand, and the Philippines. The company and its partner, Serum Institute of India, also filed for Emergency Use Listing (EUL) for NVX-CoV2373 with the World Health Organization.

There's one other major market that Novavax is targeting -- the U.S. But the company confirmed in its Q3 update that it still expects to complete its submission to the U.S. Food and Drug Administration (FDA) by the end of this year.

Novavax has been plagued with manufacturing issues that caused its filing delays earlier this year. However, the company said that it's able to produce up to 100 million doses per month as of the end of the third quarter. Novavax also believes that it's on track to reach a capacity of 150 million doses per month by year-end and expects to be able to produce over 2 billion doses annually in 2022.

2. Its valuation remains attractive

I've stated in the past that Novavax stock is absurdly cheap. That's still the case, even with shares rebounding somewhat in recent days. As of the market close on Thursday, Novavax's shares traded at 3.2 times expected earnings and 2.4 times expected sales.

Obviously, those valuation metrics assume that Novavax will generate sales and profits next year from its COVID-19 vaccine. I think that assumption is more valid than it's ever been.

Sure, it's possible that Novavax could run into snags securing the authorizations and approvals. But the company clearly thinks that it's resolved the manufacturing problems. The safety and efficacy of NVX-CoV2373 look great. While it isn't a slam dunk, it appears as if Novavax is finally in a strong position to win those much-needed regulatory nods.

3. Leading in the COVID/flu combo race 

Novavax's Q3 update also provided more reason to view the company as the leader in the race to develop a combination COVID-19/flu vaccine. The biotech has completed the enrollment of 642 healthy adults ages 50 to 70 in a phase 1/2 clinical trial of a COVID-NanoFlu combo vaccine at 10 sites in Australia.

NanoFlu already passed late-stage testing with flying colors last year. However, the company sort of put the promising vaccine on the back burner after it shifted its focus on developing a COVID-19 vaccine.

Novavax expects to report data from the phase 1/2 study in the first half of next year. That puts it well ahead of rivals. Moderna, for example, is evaluating an experimental flu vaccine in phase 1 testing. The company has also announced a new combo COVID/flu candidate but hasn't advanced it into clinical testing yet. 

There's a good chance that COVID-19 will be similar to the flu after the pandemic ends, requiring annual vaccinations. If that's the case, a combination COVID/flu vaccine would likely be quite attractive because of its convenience and potential to increase vaccination rates.

Novavax just might be the early winner in this market if all goes well with its clinical testing.