Right now, Moderna (MRNA 2.57%) generates pretty much all of its revenue from one product: its coronavirus vaccine. That was fine in early pandemic days, as strong vaccine demand equaled billions of dollars in sales every quarter.

But as we move toward a post-pandemic world, and as vaccine sales slip, investors have shied away from the biotech player. As a result, the shares are heading for a 39% decline this year.

Before you turn your back on Moderna stock, though, there's something you should know: Vaccine sales still are driving growth at this innovative biotech. Let's find out how -- and if this makes the stock a buy.

Blockbuster revenue, but lower than before

Now you might ask, "How can you say the vaccine is driving growth?" After all, sales of the product fell 94% in the most recent quarter, and even though the vaccine still should generate blockbuster revenue, it's set to come in lower than the $18.4 billion reported last year.

But it's important to look at the situation from another angle. Moderna's coronavirus vaccine sales -- in the past and today -- are helping the company fund the rest of its pipeline. Today, it holds $14.6 billion in cash and equivalents thanks to the performance of the billion-dollar coronavirus vaccine program. And this is after investments the company already has made in its growth.

For example, earlier this year, it launched its first-ever acquisition, buying OriCiro Genomics to gain access to its DNA synthesis and amplification technologies. Now called Moderna Enzymatics, the business could help cut large-scale manufacturing time by 30%, CEO Stéphane Bancel told the biopharma news site Fierce Pharma. And that could result in products reaching the market faster, a big win for patients and the biotech.

The company says it's not done with business deals and is open to other acquisitions or licensing opportunities if they can drive growth.

As for research and development (R&D) spending, Moderna says it's making this a priority as it aims to bring several products to market from 2024 through 2026. In that time frame, it could launch as many as five respiratory vaccines, a cytomegalovirus vaccine, an oncology product, and rare-disease medicines. The respiratory vaccine portfolio alone could generate between $4 billion and $9 billion in annual free cash flow by 2027, the company has said.

An 80% increase in R&D spending

So it's no surprise the biotech increased its R&D spending 80% in the first half of this year compared with the same period a year ago.

Moderna says it plans on intensifying its investments in R&D, manufacturing, and general expansion. Next year, it aims for $4.5 billion in R&D spending, up 36% from this year. The company also has made a significant effort to invest in artificial intelligence (AI), which could speed up the pace of vaccine and drug development.

Meanwhile, it is using some of its cash to buy back shares. This shows the company is confident about its future, and it reduces the outstanding share count, which could eventually lift earnings per share.

Getting back to coronavirus vaccine sales, this year the company predicts the vaccine will bring in $6 billion to $8 billion depending on vaccination rates. This plus the sales the vaccine already has generated are helping Moderna grow and eventually become a company with multiple products.

So, the vaccine still is driving growth at Moderna, and this new era could be even better than what we've seen so far. It's set to involve multiple products, and that should help steadily increase earnings well into the future.

Does this make Moderna a buy? Yes. The stock probably won't soar overnight as the market continues to focus on the decline in coronavirus vaccine sales. But this biotech company has what it takes to succeed well beyond the pandemic thanks to its vaccine and a solid pipeline of late-stage candidates. That's why now is a great time to get in on this stock and potentially score a big win over the long run.