Biotech stocks are having one of their best stretches in years. The iShares Biotechnology ETF (NASDAQ:IBB) jumped nearly 5% Wednesday and pushed to new all-time highs, according to data from Benzinga Pro.
Moderna‘s (NASDAQ:MRNA) more-than-100% surge gave the group an extra jolt, but the rally runs far wider than one headline-grabbing stock.
- MRNA stock soared on its cancer vaccine data. See the chart here.
Bespoke Investment Group’s data shows the 20 largest names in the IBB are up an average of more than 43% in 2026, with only two sitting in the red. The two laggards tell a story worth pulling apart.
Alnylam’s Guidance Cut Turns Ugly
Alnylam Pharmaceuticals, Inc. (NASDAQ:ALNY) has shed roughly a quarter of its market value since late July, and the trouble traces back to a single earnings report.
Management cut full-year 2026 revenue guidance for the company’s Amvuttra franchise, explaining that early demand had been inflated by a rush of pent-up patients when the drug first launched.
Once that initial wave normalized, growth came in well below what Wall Street had priced in. Adding to the pressure, a rival treatment from AstraZeneca and Ionis Pharmaceuticals failed its own Phase 3 trial in July, raising fresh doubts about the broader class of drugs Alnylam’s pipeline depends on.
Multiple law firms have since opened investigations into the guidance cut, a signal that the stock’s pain may not be finished playing out in headlines even if the selling has slowed.
Insmed’s Quiet Underperformance
Insmed Inc. (NASDAQ:INSM) rounds out the list as the only other red name among IBB’s top 20 holdings. Its underperformance stands out precisely because it is so rare this year — nearly every other major biotech name has participated in the upswing, from Moderna’s cancer-vaccine breakout to steadier gains across the sector’s large-cap names.
The contrast raises a fair question for investors sifting through the rally. Sector-wide strength can mask company-specific damage, and Alnylam’s selloff looks driven almost entirely by its own numbers rather than any pushback against biotech broadly.
Whether Alnylam and Insmed eventually rejoin the group’s advance may hinge on catalysts specific to each company — a pipeline update, a legal resolution — rather than any tailwind the rest of the sector is currently enjoying.
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