September's been a lousy month for biotech stocks with the Nasdaq Biotechnology Index down around 5.7% since the end of August. Rising interest rates are the main cause for concern, but that isn't a good reason to lose faith in this particular industry.

You could sit around feeling sad about the September sell-off, or you could take advantage of some bargain stock opportunities. Analysts on Wall Street who follow these three biotech stocks think they're trading for a lot less than they should be. Here's why they could be terrific bargains right now.

Wall Street analysts making price targets.

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BioCryst

BioCryst (BCRX) shares have already doubled in 2021, and the Wall Street analysts who follow the rare disease drugmaker think it can go a lot higher. The consensus price target for BioCryst at the moment represents a 44% premium.

Shares of BioCryst made a big leap after the FDA approved Orladeyo, the company's first drug, to treat a rare blood condition called hereditary angioedema (HAE) last December. The biotech stock has been holding steady for a few months as investors play wait-and-see regarding the Orladeyo launch. 

Sales of Orladeyo in the second quarter came in 161% higher than the previous three-month period to reach an annualized run rate of around $114 million. That's encouraging, but still miles behind the market leader Takhzyro, an injection for HAE from Takeda (TAK -0.31%) that earned approval in 2018.

Global Takhzyro sales grew just 6% year over year to an annualized $916 million during Takeda's most recently reported quarter. Another round of quarterly reports that show Orladeyo pushing Takhzyro out of the top spot could push BioCryst stock much higher.

Scientist pipetting under a fume hood.

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CRISPR Therapeutics

CRISPR Therapeutics (CRSP 0.34%) is down around 44% since the gene-editing stock peaked in January. While the stock may have gotten ahead of itself, Wall Street analysts are expecting it to bounce back. The consensus price target on CRISPR Therapeutics suggests a 45% gain just up ahead.

At recent prices, CRISPR Therapeutics' market cap is still up around $8.5 billion. That's an awfully big valuation for a company that doesn't have any commercial-stage products generating revenue yet. 

In April, Vertex Pharmaceuticals agreed to lead the global development of CTX001, CRISPR Therapeutics' lead candidate. This is an experimental gene therapy for sickle cell disease and beta-thalassemia. In order to raise its share of potential profits from 50% to 60%, Vertex handed CRISPR Therapeutics $900 million upfront plus another $200 million milestone payment if CTX001 earns approval in the U.S. or EU.

In June, the partners shared remarkable top-line results from the first 22 patients with at least three months of follow-up observation following a single administration of CTX001. So far, none have had to fall back on the blood transfusions they previously relied on.

Happy scientists in the lab.

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Vertex Pharmaceuticals

Vertex Pharmaceuticals (VRTX -0.06%) shares are down around 34% this year. Analysts following this highly profitable biotech think it can swiftly rebound and then some. The average target on the rare disease drugmaker is around 44% above recent prices.

Sales of Vertex Pharmaceuticals' cystic fibrosis drugs are off the charts. Second-quarter revenue soared 62% year over year to an annualized $6 billion.

The stock has stumbled because investors are worried about the company's weak internal pipeline of new drugs. A pair of clinical trial failures with candidates for the treatment of a rare genetic disorder called alpha-1 antitrypsin deficiency have pressed the stock down to a bargain bin price.

Shares of Vertex Pharmaceuticals have been trading at just 14.9 times forward earnings expectations. At this low multiple, Vertex's cystic fibrosis franchise has enough steam to deliver market-beating gains, even if its internal pipeline continues to fizzle.