Moderna (MRNA 2.70%) is the name behind one of last year's top-selling pharmaceutical products. I'm talking about its coronavirus vaccine. The company generated $18.5 billion in revenue in that first full year of sales. That's great -- but it also has investors worrying about what comes next.

After all, a good deal of the population is now fully vaccinated. And experts predict the pandemic may soon shift to an endemic situation. Does that mean Moderna's sales will plunge? Not necessarily. In fact, Moderna's best days may not be in the past -- but in the future. Let's find out why.

The past and the present

First, a quick look into the past and at the present. Moderna's vaccine stepped onto the scene only a couple of weeks behind that of bigger rival Pfizer. The two have dominated the coronavirus vaccine market. Regulators have authorized their vaccines for use in adults and children. And most recently, they've given the nod to the companies' strain-specific boosters.

Moderna forecasts $21 billion in vaccine sales this year. That's even higher than last year's sales figure.

Now let's look into the future. Various things will change in a post-pandemic world. Instead of selling doses to the government, for example, Moderna will sell the vaccine to distributors. That means Moderna will enter the private market. With fewer government contracts, we may not have as much visibility way in advance regarding sales for the year.

But we aren't completely in the dark regarding sales potential. Moderna recently said the U.S. coronavirus vaccine market post-pandemic could be worth $5.2 billion to $13 billion. The exact figure depends on vaccine uptake and pricing. And we don't yet have estimates for the worldwide market.

So, it's very possible Moderna's vaccine revenue will decline from today's level. But there are two bits of good news here. First, it probably will remain at blockbuster level. And second, now we're talking about recurrent revenue. The idea is that a certain population will go for the coronavirus booster every year -- just like the flu shot.

A high level of recurrent revenue is something to cheer about. But there's a second, bigger reason why the post-pandemic world may be even better for Moderna. That's because Moderna probably won't be a one-product company for very long.

Preparing for product launches

During Moderna's recent research and development day, CEO Stéphane Bancel said that "we are preparing for multiple product launches globally."

There are three that may be very close, and they're outside of the coronavirus program. So, they may not only offer fresh revenue sources, they will also expand Moderna's business beyond one specialty.

Moderna's investigational vaccines for flu, respiratory syncytial virus (RSV), and cytomegalovirus (CMV) are each in phase 3 trials. Bancel has said that if all goes smoothly, the flu and RSV candidates may reach commercialization in the coming two to three years.

Flu represents a $5 billion to $6 billion market. And RSV for older adults represents a greater than $10 billion market opportunity. The flu market is crowded, with big pharma Sanofi as a leader. But Moderna's goal is to develop a highly efficacious vaccine that it can quickly update according to the latest strains. If it can beat others when it comes to efficacy and speed, it may win big.

As for RSV, a commercialized vaccine doesn't exist right now. So Moderna could have a shot at dominating the market.

Moderna recently created a new role within its executive committee to prepare for new product launches. So it's clear the biotech is making the commercialization of new products outside of the coronavirus business a priority.

Will revenue soar?

Let's imagine that Moderna continues to generate coronavirus vaccine revenue and launches at least the flu and RSV candidates in the coming three years. Will revenue meet or exceed the company's current vaccine revenue?

Now, let's imagine the U.S. coronavirus market reaches the highest estimate of $13 billion -- and Moderna takes about $6 billion of that. Next, let's say Moderna takes about $2 billion in flu market share and a bit more than half of the RSV market -- that would be $7 billion. All of this totals about $15 billion.

This is still short of today's coronavirus revenue. But it's getting close. And we haven't added in international coronavirus vaccine revenue or other close-to-market products like the potential CMV vaccine.

Of course, this is just a general estimate based on what we know now. Figures could come in lower or higher. Or Moderna could face bumps along the road to commercialization.

But considering all that we know today and Moderna's late-stage candidates, the company does have what it takes to progressively generate today's revenue levels from multiple products instead of just one.

If this does indeed happen, Moderna will represent less risk for investors -- it's always better to depend on several products instead of one. The post-pandemic world will indeed be a better one not only for you and me, but also for Moderna and its investors.