There's no time like the present for biotech stocks, especially those of companies engaged in coronavirus vaccine development. Between the yet-to-be-contained pandemic and a newfound global appreciation for preventative care against infectious diseases, it's a no-brainer why vaccine manufacturers are leading the biotech charge once again.

The two companies I'll discuss today are primed to surge this summer thanks to powerful catalysts, and they're both tackling many of the same projects to pave the way for future growth. While it's true they're both on the pricey side at the moment, investors can take heart in the long-term staying power that these stocks have, and that's what makes them worthwhile purchases.

Two biologists talk at a laboratory bench while one is in the middle of an experiment.

Image source: Getty Images.

1. Moderna 

Though it may seem a bit overpriced at the moment, Moderna (MRNA -0.46%) is still worth buying sometime this summer, because its impressive revenue from coronavirus vaccine sales could just be getting started. On May 12, it signed a deal with the government of Australia to provide 25 million vaccines through 2022. But that's small potatoes compared to the new orders that will roll in if its candidate is approved for use in teenagers, which the company is investigating in clinical trials right now.

Three months into the year, the company had already made $1.7 billion, which accounts for sales of only 102 million doses. International revenue has barely started to ramp up, and management expects around $19.2 billion in sales from the advance purchase agreements that are already on the books. In total, the company expects to make up to 3 billion doses in 2022. It's reasonable for investors to expect reports of piles of revenue and plenty of stock price appreciation in return.

Then there are the catalysts that are a bit less certain. If coronavirus variants continue to circulate, it's likely that people will need booster shots to protect them in the short term, subsequently increasing the number of doses sold per person. Research into using a single booster shot of the vaccine's original formulation is already in phase 2 clinical trials, and management reported on May 5 that the preliminary results look favorable. Similarly, Moderna is investigating a variant-specific booster shot regimen with a slightly different formulation which appears to be even more effective. Protection against variants aside, there's also the issue of whether Moderna's vaccine might need yearly top-ups to stay effective, which would make its eye-popping revenue into a recurring feature. And of course, Moderna has an entire pipeline of medicines that are in various stages of development.

While those projects probably won't add to the top-line growth anytime soon or at the same scale as the coronavirus vaccine, they'll secure the company's innovative reputation, not to mention its post-pandemic future. There's just one issue that potential investors need to be cautious about. At the moment, the stock's valuation is quite expensive, given that the biotech industry's average price-to-sales ratio is around 8, whereas Moderna's is just over 23. So, keep an eye out for any dip in the market that could be a favorable purchasing opportunity, though there's no guarantee one will ever come.

2. Novavax

Because it's also making a coronavirus vaccine, Novavax (NVAX -1.91%) is a compelling stock for many of the same reasons as Moderna. Unlike Moderna, however, its candidate doesn't have regulatory approval yet. The company plans to file for approval in the third quarter of 2021, and it's highly likely that regulators will give it the green light shortly thereafter, clearing the way for organic revenue growth to start with gusto. There are already 200 million doses accounted for by advance purchasing agreements, so shareholders could soon revel in an escalating stock price.

In the meantime, Novavax is already testing its coronavirus vaccine in teens while evaluating the need for booster regimens in light of coronavirus variants. By the end of the year, it'll be making at least 150 million doses per month. So far, so good -- but why not just buy Moderna instead? 

Novavax has one big thing going for it that Moderna doesn't: The potential for near-term flu vaccine revenue. Its NanoFlu vaccine for older adults isn't approved for sale yet, but it sailed through its final clinical trials and is awaiting submission to regulators. When management opts to move the project forward to commercialization, the company will gain a significant and seasonally recurring income stream. That might not seem very juicy, given the ongoing global pandemic caused by a different virus, but it's important to remember that influenza didn't go extinct just because the coronavirus showed up. People will need flu vaccination just as much as they always have, especially as mask mandates and other protective restrictions ease. 

Moving forward, expect the company to try to fold its successful coronavirus vaccine and its successful influenza vaccine into one unified jab. Investors might need to wait a few years for the combination to hit the market, given that it's only in preclinical studies at the moment. Nonetheless, the convenience of such a product could make it a best-seller -- and that's why it's worth buying the stock today, before the market has had a chance to price in the expected revenue.