Anyone who bought Novavax (NVAX -2.71%) stock prior to 2020 and sold at the end of last year scored a big win. The stock surged more than 3,400% over the past two years because investors bet on the company's coronavirus vaccine candidate.

But in recent times, stock performance hasn't been so bright. Why? Investors lost interest in the biotech company when it fell behind in its regulatory requests.

Today, Novavax is back on the right track. It's won authorization in more than 35 countries and is awaiting a regulatory decision from the U.S. Does this mean it's a good time to buy shares? Or is top share performance a thing of the past? Let's find out.

A healthcare worker vaccinates a person in a medical office.

Image source: Getty Images.

In a post-pandemic world

Novavax reached the vaccine market about a year later than market leaders Pfizer and Moderna. But it's important to keep in mind that the coronavirus vaccine isn't a one-shot deal (excuse the pun).

The virus will stick around, even in a post-pandemic world, experts say. At least the most vulnerable individuals will need protection. This means vaccine revenue represents a long-term opportunity -- and that may equal billions of dollars for latecomers such as Novavax.

Now, a look at the current picture. Novavax has orders for 110 million vaccine doses from the U.S. and has won orders for as many as 430 million doses from various countries around the world. Novavax also signed agreements for 1.1 billion doses for low- and middle-income countries. These countries don't pay as much for vaccines as higher-income countries, but the company could gain over time through the sheer volume of product needed in these locations.

In other positive news, Japan just became the first country to give the Novavax product the nod for use as a primary vaccine and as a booster. The booster market could be an important one for Novavax -- especially since experts have approved the idea of "mixing and matching" vaccine brands. As for this year, Novavax expects to generate $4 billion to $5 billion in revenue due to vaccine sales.

Of course, that sales figure doesn't come close to the $32 billion and $21 billion that Pfizer and Moderna have respectively predicted for their vaccines. But that's OK. If Novavax can maintain a blockbuster level of revenue for this -- its first and only commercialized product -- for a few years, that's a huge deal.

The next big product

Novavax may be the leader when it comes to the next big vaccine product. I'm talking about a combined coronavirus and flu vaccine. The company reported positive data from a phase 1/2 trial of the candidate this week and plans to start a phase 2 dose confirmation trial by the end of the year.

Moderna also is working on a combined vaccine candidate but hasn't yet started clinical trials. So Novavax has an edge from a timeline perspective because it already has a fully developed flu vaccine candidate. It's called NanoFlu and has met all primary endpoints in a pivotal trial.

This and Novavax's coronavirus vaccine are components of the combined vaccine. Moderna's flu vaccine component still is involved in clinical studies.

The idea here is that a combined vaccine could interest a great deal of the population -- for instance, those who regularly go for flu shots. Last year, that was about half of the U.S. population.

Now let's get back to our question about Novavax stock. Is it too late to buy?

If you're looking for a 1,000% or more gain in a year or less, the answer may be yes, it's too late. Investors' interest in the vaccine theme seems to be waning at this stage of the pandemic, and it's unlikely to pick up post pandemic.

But if you're a long-term investor looking for gains over time, it's definitely not too late to buy Novavax shares, especially at today's price. Right now, the stock is trading at only 2.28 times forward earnings estimates.

As I said above, vaccine revenue isn't likely to disappear any time soon. In fact, a potential combined vaccine could become a source of recurrent revenue. Eventually, this should win over more investors -- and reward those who hung onto this biotech stock for the long haul.