What happened

Shares of Biogen (BIIB 0.23%) were sinking 10% this week as of the market close on Thursday. The slide came after the company's CEO stated on Thursday that the launch of Alzheimer's disease drug Aduhelm has been slower than expected.

So what

Biogen CEO Michel Vounatsos spoke at the Morgan Stanley 19th Annual Global Healthcare Conference on Thursday. He said that only around 50 centers in the U.S. have given at least one dose of Aduhelm so far. That's a dismal rollout, considering that the U.S. Food and Drug Administration approved the Alzheimer's disease drug more than two months ago.

Vounatsos attributed the slow start to "confusion, misinformation, and controversy" surrounding Aduhelm and its FDA approval. The FDA's own advisory committee voted overwhelmingly against recommending approval for the drug. Many in the scientific community have spoken out in opposition of the U.S. approval as well.

A document with "Alzheimer's disease" printed on it next to X-rays, a pen, syringes, and pills.

Image source: Getty Images.

In Biogen's second-quarter conference call, director of investor relations Mike Hencke said the company is assuming only "modest" sales from Aduhelm in 2021. Those sales could be even more modest than Biogen anticipated. Vounatsos said on Thursday the company is revisiting its "already very low sales target" for this year.

Now what

After this week's decline, Biogen's shares are now down close to 27% below the highs set after the FDA approved Aduhelm. The best way for the biotech stock to recover is for Biogen to post solid overall sales growth. But with a sluggish launch for Aduhelm, such growth will likely take longer than investors would like.