The stock market has been performing better recently, with the S&P 500 up by nearly 5% in the past three months, although it remains down 18% over the past year. Will this mini-rally extend well into 2023? It's hard to say. Economic or market conditions could worsen and drag down the stock market.

Regardless of potentially unforeseen dynamics that could affect equity markets in 2023, investors should continue to invest in solid stocks that can grow long after the current downturn is behind us. That's an excellent way to record strong returns over time.

With that said, let's consider two growth stocks worth buying in 2023: Axsome Therapeutics (AXSM 1.36%) and Novavax (NVAX 2.31%).

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1. Axsome Therapeutics

Axsome Therapeutics focuses on developing therapies that affect the central nervous system. In August 2022, it earned approval for Auvelity, a treatment for depression. Auvelity is a fast-acting option that has proven to address symptoms of depression in patients, with long-lasting results. It comes at a time when depressive symptoms rose during the pandemic.

The biotech's lineup also includes Sunosi, which targets daytime sleepiness in narcolepsy patients. Axsome acquired Sunosi from Jazz Pharmaceuticals in May 2022. For Axsome, the approval of Auvelity in treating depression was just a first step. It is looking to earn label expansions for this medicine in targeting Alzheimer's disease agitation and smoking cessation. The company has several other programs as well.

It could be easy to dismiss Axsome Therapeutics because of its financial results. In the third quarter, it earned total sales of only $16.8 million and did not record any revenue in the comparable period of the previous fiscal year. On the bottom line, its net loss came in at $44.8 million, worse than the $34.9 million reported in the year-ago period.

But Axsome Therapeutics is still in the early innings of its growth potential.

It should earn several new approvals and label expansions in the next three years while Auvelity gains traction in patients with depression. Axsome's prospects partly explain how its shares doubled this year. The company may not pull off a performance like that in 2023. But that shouldn't matter to investors focused on the long game.

What matters more is that the company boasts a product that could achieve sales above $1 billion at its peak and promising programs that could lead to breakthroughs. Those ingredients can help any biotech company succeed in a relatively long period of five years or more, and Axsome Therapeutics is in an excellent position to reach that goal.

2. Novavax 

Things keep getting worse for Novavax. The biotech is a latecomer in the coronavirus vaccine market, where other companies have already gotten much of the spoils. It is true that Novavax's candidate, Nuvaxovid, has earned approval or authorization in dozens of countries worldwide. But now that the worst of the pandemic seems to be in the rearview mirror, the need for vaccines has declined. 

And to make things even more difficult, Novavax recently resorted to a public offering of common stock, a move that sank its share price even more. The biotech's stock is down by 95% in the past year.

But Novavax's shares have gotten too cheap, and that's why they are worth buying right now. The company currently sports a minuscule market capitalization of $753 million. For context, the company expects total revenue of about $2 billion this year. And on average, analysts forecast that it will generate $1.34 billion in sales next year.

Even remotely approaching this projection would be relatively impressive for a company whose market cap is well below $1 billion. Novavax's hopes in the booster market will be important moving forward. The company expects the annual booster market size after 2023 will be roughly 225 million people, much larger than the flu market in the country of between 170 million to 190 million people.

Of course, it will also look to profit from the coronavirus booster space in other countries. At its current levels, it won't need to generate tens of billions per year from Nuvaxovid for the vaccine to be considered a success; even half a billion dollars per year would do the trick. And that's before we account for Novavax's other candidates, including a combined COVID-19/flu vaccine in a phase 1/2 clinical trial, and a malaria vaccine in a phase 2 study.

In my view, the market is severely undervaluing Novavax's prospects, which constitutes a good reason to buy the company's shares.