A stock that trades at $15 or less isn't necessarily a bargain. Often, a stock trading that low is risky and anything but a bargain. However, biotech stocks Novavax (NVAX 2.95%), MannKind (MNKD 1.22%), and Anavex Life Sciences (AVXL) all trade at $15 or less a share, and I see the potential for substantial upside for all three.

Novavax stands out with its more traditional, protein-based COVID-19 vaccine; MannKind is making a name for itself with inhaled therapies for diabetics and patients with lung disorders; and Anavex has a promising Alzheimer's therapy. Let's take a closer look at each one.

1. Novavax sees positive signs

New year, new CEO, new vaccine. That's the mantra for vaccine maker Novavax, which has seen its shares decline more than 90% over the past year.

The company just announced that Stanley Erck, the current president and CEO, is retiring effective Jan. 23. He is being replaced by John Jacobs, who had been the president and CEO of Harmony Biosciences since 2018. In his time there, Jacobs oversaw a company that had a successful initial public offering and went from a clinical-stage biotech to a commercial one.

Last year, Harmony had $117 million in revenue, up 9% year over year, and earnings per share (EPS) of $1.48, up 270% over 2021.

The announcement was enough to give Novavax stock a boost, but whether that rise lasts depends on the outlook for NVX-CoV2373, the company's protein-based COVID vaccine (as opposed to a messenger RNA-based vaccine). Novavax has also been working on a combination COVID-19-influenza vaccine. This is in a phase 2 trial and may make sense to insurers and patients who would rather have one annual shot than a separate COVID-19 and influenza shot.

The COVID-19 pandemic may have waned, but the way the virus has constantly mutated into different variants will likely mean COVID vaccinations will be needed for years. The company said it sees the COVID vaccine market continuing to be a multibillion-dollar business.

Novavax could use a shot in the arm financially. It said it expects total revenue this year of $2 billion, compared to $1.6 billion last year. Over the past five years, it has grown revenue by 3,240%. That's the good news. The bad news is Novavax hasn't been profitable and has lost $475.7 million through nine months -- though that's a better pace than the $1.74 billion it lost in 2021. 

At its current price, the stock could be worth the risk. Its price-to-sales ratio has fallen to 0.4, compared to 8.6 a year ago.

2. One big step for MannKind

MannKind's shares are up more than 30% over the past year. The company specializes in inhalable therapies for patients with endocrine disorders and with orphan lung diseases.

Through nine months, MannKind reported revenue of $63.7 million, up 1.2%, year over year. However, over that same period, it also lost $69.5 million, or $0.27 in EPS, compared to a loss of $52.8 million, or an EPS loss of $0.21 in the same period a year ago. 

MannKind's lead therapy, Afrezza, an inhalable form of insulin, brought in nine-month revenue of $31.3 million, nearly half of the company's total and representing a 13% climb year over year. 

What's more exciting is that the company has another product that could surpass Afrezza in sales. MannKind is partnering with United Therapeutics on Tyvaso DPI, a therapy to treat pulmonary arterial hypertension (PAH) that uses small inhaler cartridges. United pays MannKind to make Tyvaso DPI, and MannKind gets royalties on United's sales of the product. In the first full quarter of the collaboration, MannKind received $15.8 million from Tyvaso-related sales, and that doesn't include some royalties that were deferred.

Another driver of income is the company's $10 million purchase of the V-Go once-daily wearable insulin delivery system, worn like a patch, from Zealand Pharma. MannKind reported third-quarter net revenue of $5.4 million from V-Go, up 28% quarter over quarter, and the company said it expects full-year V-Go sales of between $18 million to $22 million.

3. Anavex's Alzheimer's therapy shows promise

Anavex's stock is down more than 22% over the past year, though it is up more than 28% the past month. The clinical-stage biotech focuses on treating central nervous system diseases.

It doesn't have any revenue yet, but it does have an encouraging Alzheimer's drug candidate in Anavex 2-73 (blarcamesine). With news from the Food and Drug Administration's approvals of Alzheimer's therapies Lecanemab (made by Biogen and Eisai) and Aduhelm (made by Biogen), Anavex's therapy has perhaps gotten lost a bit. 

However, in initial reports from its phase 2/3 study, the company said that Anavex 2-73 reduced cognitive decline on the Alzheimer's Disease Assessment Scale (ADAS)-Cog scale by 45%, compared to a placebo. That's better than Lecanemab, which reduced cognitive decline by 27%, and Aduhelm, which showed a 1.4% difference. On top of that, Anavex 2-73 is a pill, while Lecanemab and Aduhelm are administered by injection.

Still, the drugmaker needs more extensive results from the trial to prove Anavex 2-73's safety and efficacy, and the bar is set high for after the controversy surrounding Aduhelm's approval in 2021.