Right now, Moderna (MRNA -1.39%) is generating billions from its coronavirus vaccine. But this innovative biotech company has its eye -- and research -- on another big opportunity. And it soon may find itself in a second billion-dollar market. That's the flu market.

Wait a minute, you may be saying. The flu? When you think of flu vaccines, you may not necessarily think of a huge market opportunity. Many players already share the market. And no one talks about flu vaccines as representing blockbuster revenue. But there may be more to this market than first meets the eye. Let's find out why this may be Moderna's next success story.

Today's flu market

First, a look at today's flu market. It's worth about $5 billion to $6 billion. U.S. health officials recommend nine flu vaccines for use during the upcoming season. Four different pharmaceutical companies make these vaccines. Market leader Sanofi generated $2.6 billion last year from sales of its flu vaccines.

So, how could a new player make a big mark on this scene? Well, the market is evolving. And it's moving toward the idea of better and more effective vaccines. For example, a vaccine targeting the very latest flu strain in a particular country. Or even a combination vaccine that targets both flu and another virus -- such as the coronavirus. Moderna is working on both.

The company's flu candidate recently began a phase 3 study. Farther down the road, Moderna's big goal is to commercialize combination respiratory vaccines. The company is studying a coronavirus plus flu vaccine candidate in phase 1. And it's exploring a candidate covering flu, coronavirus, and respiratory syncytial virus in preclinical studies. Moderna expects that candidate to start phase 1 trials by the end of the year.

Combined vaccines represent a huge opportunity. That's because people are likely to prefer getting one series or individual shot that covers two or three viruses over going out for multiple shots. And healthcare providers will gain in efficiency.

"Premium" vaccines

Getting back to the issue of more targeted efficacious vaccines, Moderna says these "premium" vaccines could result in a larger flu vaccine market overall. And the company says these vaccines merit higher prices -- for instance, more than $50 per dose. For the upcoming flu season, shots range between $18 and $28 per dose.

All of this means the flu opportunity of tomorrow may be much different from the flu market of a few years ago -- or even today. And Moderna could be among the first to benefit. Moderna has said it may launch three respiratory vaccines within the coming two to three years. And one of those is the flu candidate.

At the same time, Moderna predicts the annual coronavirus vaccine market in the U.S. alone may range from $5.2 billion to $13 billion. The exact number will depend on vaccine pricing and uptake among the population. But even at the low end, Moderna still has ensured itself one blockbuster product.

If all goes well with the flu candidate, Moderna may add a second blockbuster vaccine to its repertoire.

What does this mean for investors?

Moderna may be on the road to dominating not just one, but two billion-dollar vaccine markets in the next few years. Considering this, Moderna's price of 5.2 times forward earnings estimates looks pretty cheap.

Of course, Moderna shares may not soar in a short period of time like they did at the start of the pandemic. But for long-term investors, that's OK. Over time, Moderna may prove that its first product will continue to thrive. And at the same time, the company might excel in and transform other major markets.

So, right now is a great time to buy or hold Moderna shares -- and watch the company enter an exciting new chapter.