Moderna (MRNA -3.36%) generated billions of dollars from its sale of coronavirus vaccines earlier in the pandemic. Today, most of the people who wanted the primary vaccine series have gotten it. But that doesn't mean Moderna's revenue opportunity is over.

The biotech's next revenue driver is selling a strain-specific booster. Regulators gave the omicron booster a thumbs-up this summer. And the product made it to market in time for the fall vaccination season. Still, one particular number doesn't look so brilliant. Could it mean trouble for Moderna?

The strain-specific booster

I'm talking about the number of people who have received Moderna's strain-specific booster. The U.S. Food and Drug Administration (FDA) recently extended its authorization of the booster to include people ages six and older. But initially, the FDA gave the nod only for use in adults. So, we'll look at the percentage of adults who have received Moderna's updated shot.

Of the adults who have completed a primary vaccine series, less than 3% have opted for a Moderna booster so far. The Centers for Disease Control and Prevention (CDC) generally recommends people go for flu shots before the end of October. So, if we use this as a guide, it's clear that a very small percentage of the population has opted for the updated booster.

Before we get too worried about Moderna's fate, though, it's important to keep in mind a few points. First, like flu, the coronavirus may eventually become seasonal. We have seen the biggest peaks in cases during the winter months.

But we've also seen smaller peaks during other times of the year -- such as spring and summer. This may spur people to get booster shots at times outside of the usual fall season, at least for now.

Second, the FDA has recommended the updated booster for those whose last coronavirus shot was at least two months ago. Many of the most fragile people have gotten vaccination as frequently as possible. Some of them may have received a booster a short while ago. Therefore, they may have to wait before getting the updated booster. So, we could see a peak in booster uptake in a few weeks as these people become eligible.

Moderna's future

Of course, all of this is unlikely to lead to a huge jump this year in the numbers of people opting for strain-specific boosters. But I'm still not overly worried about Moderna's future.

Here's why. About half of the U.S. adult population that got a primary series has gone for a first booster dose. These are the products that were available before the strain-specific boosters. Many of these people -- if they aren't high-risk -- probably feel sufficiently protected for now. They might wait until next flu season to go for another shot.

The coronavirus booster might take the same path as the flu vaccine when it comes to uptake. But we may not see that clearly until next year.

So, today's booster number doesn't necessarily spell trouble for Moderna. The company is still fulfilling its government contracts right now. The number of doses administered today won't change that revenue. And the uptake of first boosters could be hurting demand for this new strain-specific booster. But this is a temporary issue.

What does this mean for investors?

The booster uptake number doesn't change my positive view of Moderna. The company is preparing for its post-pandemic vaccine business right now. Boosters probably won't replicate the enormous revenue levels of vaccines at the start of the pandemic.

They still could be blockbusters, though -- and they can become a steady source of annual revenue. This is important because it could help Moderna advance its broad pipeline of potential products. As it stands, the $18 billion in cash Moderna already has thanks to the vaccine is a huge advantage.

Moderna's shares may not immediately rebound from this year's losses. But boosters and other potential products on the horizon could make Moderna and its investors long-term winners.