There's an old cliche which says that opportunity only knocks once. But if you're bummed that you missed out on buying shares of Moderna (MRNA -10.05%) sometime during its run-up of 373% over the last three years, all is not lost. The biotech company is working on plenty of other potential products in its pipeline that could send its stock higher again -- and it (hopefully) won't need to create a vaccine for an emerging global pandemic this time around.

Here's what's coming and what you need to know before investing. 

Expect new vaccines on the market

The Moderna of early 2028 will almost certainly have a few more products on the market than it does today. Aside from updates to its coronavirus vaccine, it could also be selling jabs for influenza, respiratory syncytial virus (RSV), cytomegalovirus (CMV), and perhaps even a couple of other infectious diseases too, not to mention combination vaccines that inoculate against multiple common viruses at once. It's also working on a much-vaunted personalized cancer vaccine (PCV) in phase 2 trials in collaboration with Merck that could revolutionize treatment of cancers like melanoma.

Making the jump from prophylactic vaccines to therapeutic vaccines will be a major hurdle, and Moderna's stock could shoot upwards as a consequence. Even without such clinical breakthroughs, shareholders should expect to keep getting rewarded with share buybacks over the next few years, and it's likely that the biotech will gobble up some smaller businesses to build out its platform along the way.

By 2028, Moderna could look a lot more like a traditional large pharma, with a core platform that's consistently getting augmented with tack-on acquisitions and an early stage pipeline comprised of assets poached from younger biotechs. 

In terms of financial performance, the effect of getting several of its existing sets of programs out the door would cement the company's status as a leader in biopharma research and development (R&D), but it'll still be hard to top the $18.4 billion in coronavirus vaccine sales it reported for 2022.

And while entering the commercial market (rather than solely taking purchase orders from governments) with its coronavirus jab sometime in the next couple of years will prevent revenue from flatlining entirely, it's practically guaranteed that its top line will be shrinking for a while. So don't be shocked if its stock retreats even if the company is reporting positive results from its most promising clinical projects.

Don't be surprised if blemishes start to show

As promising as Moderna's long-term future is, investors should also be realistic about the probability of setbacks, some of which might be significant.

Of particular concern is the foundational mRNA vaccine technology that's at the core of the company's value. At present, the limitations of the mRNA vaccine platform are not entirely understood, though they are coming into somewhat clearer focus. The most important issue so far is that the coronavirus jabs appear to confer low durability of protectiveness against symptomatic infection, which in English means that they don't elicit long-lived immunity that would prevent people from getting and feeling sick.

It's unclear whether that problem is a result of the slipperiness of the coronavirus and its ability to continue to mutate, or whether it's a feature of Moderna's approach -- or both, or some other combination of causes. Time will probably clarify the issue, and it might damage the biotech's share price in the process if the conclusions aren't favorable. It's also very possible that the issue can be addressed effectively with further development of the technology.

Beyond that, there is also a good chance that one of Moderna's 48 other programs in the pipeline will report worse-than-anticipated results sometime in the next five years. Such bumps in the road are fully expected in biotech, and they don't necessarily herald any kind of broader decline in a business' competitive ability, but they could still spook investors and damage the stock, potentially by a large amount.

With these caveats in mind, Moderna is still likely to be one of the leading biotechs in 2028. Sitting like a dragon atop a resplendent treasure pile of $18.2 billion in investments, cash, and cash equivalents, the company can afford to whiff quite a few of its attempts to commercialize new medicines before its operations will be under significant financial pressure.

While its next couple of years may be a bit challenging as a result of receding coronavirus jab sales, it's hard to see how its stock could be worth less in the future compared to today.