Coronavirus vaccine stocks skyrocketed last year. Players like Novavax (NASDAQ: NVAX) and Vaxart scored the biggest wins, each climbing more than 1,500%. Investors placed bets on the companies most likely to bring a vaccine to market -- or make a splash with innovative technology. These days, three vaccines have entered the market -- from Pfizer, Moderna (NASDAQ: MRNA), and Johnson & Johnson. We're no longer betting on which companies will make it to the finish line first. But that doesn't mean the opportunity to invest in coronavirus vaccine stocks is over. Far from it. Two things are set to drive massive gains in these stocks over the long term. What are they? Product revenue and the development of newer vaccines or boosters to handle emerging coronavirus strains. And two stocks are likely to deliver both in the coming months and years, so an investment in them could double your money. Which companies are these dynamic vaccine makers? Image source: Getty Images. Moderna Moderna shares climbed 434% last year, but that's just the beginning of this stock's story. The U.S. Food and Drug Administration (FDA) granted Moderna's vaccine candidate Emergency Use Authorization (EUA) in December. In just two weeks, the vaccine brought in more than $199,000 in revenue. And advanced purchase agreements signed so far promise $18.4 billion in revenue this year. That's a big deal for a company that didn't have any product revenue prior to the vaccine launch. Shares aren't expensive right now if we consider earnings potential. The stock is trading at less than six times forward earnings estimates. MRNA PE Ratio (Forward) data by YCharts. The biotech company also is looking good when it comes to handling coronavirus variants. Moderna said its vaccine protects against the U.K. and South African strains. But today's vaccines -- including Moderna's -- still lose some efficacy against these variants. That's why the company is charging ahead to develop a more precise product. Moderna just dosed the first volunteers in a study of strain-specific boosters. The trial is testing a booster candidate targeting the South African strain, one combining the authorized vaccine and the booster, and an extra dose of the authorized vaccine. And the great news here is the FDA said it won't require extensive clinical trials for vaccine updates or boosters from companies with an authorized vaccine. That speeds up time to market. Novavax You might be skeptical when I tell you that Novavax still has potential to climb. That's because the shares surged 2,700% last year. But that was before Novavax announced phase 3 trial results and its plan to handle strains of concern. These elements and Novavax's massive production network mean the clinical-stage biotech might be on its way to becoming a coronavirus vaccine giant. Novavax's U.K. phase 3 trial showed the vaccine is 96% efficacious against the original coronavirus. That beats leaders Moderna and Pfizer. They reported 94.1% and 95% efficacy, respectively. Against the U.K. strain, Novavax demonstrated 85.6% efficacy. And a phase 2b trial showed the candidate is 60% efficacious against the South African strain. The trial took place in South Africa, where the variant made up 90% of coronavirus cases. These results are strong, but Novavax is taking things a step further. Like Moderna, it's working on a candidate to target emerging strains. The company plans to launch trials by the middle of this year. If and when Novavax brings a vaccine to market, it has the capacity to produce. It's ramping up to make 2 billion doses annually as of midyear. That's higher than Moderna's goal for 700 million to 1 billion doses this year. When can we expect revenue? Possibly by this summer. Novavax will report data from a U.S. phase 3 study in the coming weeks. And the company expects to complete its EUA request in the second quarter. A Novavax vaccine could be on the market a few weeks after that filing -- if the FDA likes what it sees. Considering Novavax's profit potential, the shares aren't expensive. They're trading at a little more than six times forward earnings estimates. NVAX PE Ratio (Forward) data by YCharts. When will these stocks double your money? First, keep this in mind that it may not happen. If the FDA doesn't authorize Novavax's candidate, the shares would probably crash. And if Moderna's strain-specific booster program fails, the stock would surely drop. Both stocks are extremely dependent on the companies' coronavirus vaccine programs. But if all goes well, these biotech stocks have all that it takes to double your money. Whether it's this year or in the not-too-distant future, Moderna and Novavax are looking at billions of dollars in annual revenue. They both also have solid pipelines of other product candidates that may add to revenue later on. That makes them winning investments for the long-term investor. 10 stocks we like better than NovavaxWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Novavax wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of February 24, 2021 Adria Cimino has no position in any of the stocks mentioned. The Motley Fool recommends Johnson & Johnson and Moderna Inc. The Motley Fool has a disclosure policy.Source