Most people consider Moderna (MRNA -0.74%) a coronavirus vaccine stock. And for good reason. The vaccine is the company's only product right now. And it's generated billions of dollars in revenue and profit for this biotech player.

Moderna's status as a vaccine stock once brought it major gains. But today, just the opposite is happening. Some investors have dropped Moderna and moved on to other investment themes. But the Moderna story is far from over. And some pretty exciting chapters may lie ahead. Here are three things the smartest investors know about this beaten-down stock.

1. Vaccine sales probably won't disappear

Moderna expects $21 billion in coronavirus vaccine sales this year. That's according to advance purchase agreements with governments. Moving forward, however, sales figures probably won't be as high. In a post-pandemic world, Moderna expects high-risk individuals -- not the entire population -- to seek vaccination.

Even though Moderna plans on increasing the price of the vaccine, it's still unlikely to compensate for the loss of volume. This doesn't mean coronavirus vaccine sales will dwindle to nothing, though. Moderna recently said the U.S. market alone could reach as much as $13 billion once the pandemic is over.

It's also important to keep in mind that Moderna is working on a future product that could offer it long-term dominance and encourage more people to get a coronavirus vaccine. I'm talking about combined respiratory vaccines. The company is testing a candidate combining flu and coronavirus and a second candidate combining flu, coronavirus, and respiratory syncytial virus (RSV).

This means that coronavirus vaccination could provide a steady source of blockbuster revenue -- even if the level isn't as high as it is today.

2. New blockbusters may be around the corner

Now here's why we shouldn't be too bothered by a potentially lower level of revenue from Moderna: It probably won't last forever. Moderna has 46 programs in development. And, importantly, three non-coronavirus candidates are in phase 3 clinical trials right now.

In fact, the company says two of these candidates -- vaccines for flu and RSV -- may result in commercial launches in the coming two to three years. Both of them carry blockbuster potential. The flu market today is worth $5 billion to $6 billion. But Moderna says more efficient vaccines could increase the value of the market -- and those particular vaccines could go for a higher price than today's leaders.

Regulators haven't yet approved an RSV vaccine. GSK plc is a step ahead of Moderna. The company recently reported positive phase 3 results and plans to apply for regulatory approval this year. Moderna forecasts this market as more than $10 billion. That means there's enough room for more than one player to succeed.

So, yes, Moderna relies on the coronavirus vaccine today. But in a few years, we may be looking at a multi-product company.

3. Moderna's biggest gains may be down the road

Right now, Moderna's shares are trading for less than 5 times trailing-12-month earnings. This looks cheap. But investors worry about a point in the future when coronavirus vaccine earnings may decline -- and other potential products may not yet be on the market to compensate. Is the stock still cheap today with this in mind?

The answer from investors who know Moderna well is "yes." Of course, there probably will be a time when earnings will stagnate as we wait for the next batch of products to come to market. But if all goes smoothly, Moderna could soon commercialize its potential flu and RSV vaccines, as mentioned above. And the company's third phase 3 candidate -- a vaccine for cytomegalovirus (CMV) -- might follow.

Considering these possible products and the size of Moderna's earlier-stage pipeline, today's valuation looks like a bargain. If even a few of Moderna's pipeline programs make it to market, the company could produce major earnings a few years down the road.

And that could send the shares soaring. So, Moderna's biggest gain may not be its 2020 performance. (The stock rose more than 400% then.) Instead, it could deliver more to investors who hold on over time.