Biogen's Once-a-Year Shot Could Rewrite the Playbook for SMA

After treatment with salanersen (at doses of 40 mg or 80 mg), all 24 kids improved on at least one measure of motor function. Half of them, 12 out of 24, achieved brand-new WHO motor milestones like sitting or standing independently. Not a single child lost ground on milestones they'd already reached.

Then there's the biomarker data. Neurofilament light chain (NfL) is a protein that leaks into spinal fluid when nerve cells are dying; think of it as smoke from a fire you can't see. In children who had elevated NfL levels at the start of the trial, salanersen reduced those levels by 75% within six months, and the improvement held through at least a year of follow-up. That's a strong signal that the drug is slowing neurodegeneration, not just masking symptoms.

Safety looked reassuring, too. Most side effects were mild: upper respiratory infections, vomiting, and fever. Nothing that raised red flags at either dose level.

Why This Matters Beyond the Data

Biogen needs this win. The company's SMA franchise built on Spinraza has been under siege from two directions. Novartis' Zolgensma offers a one-time gene therapy infusion. Roche's Evrysdi is an oral drug patients can take at home. Both have chipped away at Spinraza's market share since its peak years.

Biogen's total revenue hit $9.9 billion in 2025, up a modest 2% from the prior year. But the company is forecasting a mid-single-digit decline for 2026, driven largely by erosion in its multiple sclerosis portfolio. The SMA treatment market, meanwhile, is estimated at roughly $5 to $6 billion and growing at a healthy clip, with gene therapies like Zolgensma posting the fastest growth rates.

Salanersen represents Biogen's play to stay relevant in that expanding market. A once-yearly injection that works after gene therapy has already been tried? That's a compelling pitch to neurologists and families alike. It positions salanersen not as a competitor to Zolgensma, but as a complement: the therapy you add when the initial treatment isn't enough.

The Road to Approval Is Long (and Crowded)

Promising Phase 1b data from 24 patients is encouraging, but it's a long way from an FDA approval. Small, open-label studies (where everyone knows they're getting the drug) can look rosier than reality. The placebo effect is real, and confirmation bias is a powerful force in clinical research.

Biogen is wasting no time scaling up. The company has launched three Phase 3 trials, all using the 80 mg dose:

• STELLAR-1: An open-label study in treatment-naïve, presymptomatic infants under six weeks old. These are babies identified through newborn screening before symptoms appear.
• STELLAR-2: A randomized, double-blind, sham-controlled trial (the gold standard) in infants who received Zolgensma presymptomatically. Salanersen would start about six months after gene therapy.
• SOLAR: An open-label study enrolling roughly 90 adolescents and adults aged 15 to 60. The primary endpoint is change on the Hammersmith Functional Motor Scale-Expanded, a standardized test of physical ability.

All three trials will follow patients for five years, with enrollment kicking off between Q2 and Q3 of 2026. The STELLAR-2 design is particularly important because it directly tests salanersen in the post-gene-therapy population where Phase 1b showed promise.

Wall Street Is Watching, but Not Cheering Yet

Analyst reactions to the salanersen data have been muted so far. Recent Biogen coverage from major banks has focused more on the Alzheimer's therapy Leqembi and the company's broader revenue trajectory. Goldman Sachs has a Buy rating with a $231 price target; Barclays sits at Equalweight with $185. BMO Capital recently raised its target to $196, specifically citing potential in the Spinraza franchise.

The lack of salanersen-specific commentary isn't necessarily bearish. Wall Street tends to reserve its enthusiasm (or skepticism) for Phase 3 readouts, not early-stage data in 24 patients. The real test comes when STELLAR-2 delivers blinded, controlled results that either confirm or deflate the Phase 1b story.

The Bottom Line

Biogen has a drug that could transform how doctors think about SMA treatment sequencing. Instead of choosing between gene therapy and an ongoing medication, families might eventually use both. Salanersen's once-a-year dosing is a genuine differentiator in a disease where treatment burden matters enormously, especially for children who already endure frequent medical visits.

But 24 patients is a prologue, not a proof. The next few years of Phase 3 data will determine whether salanersen becomes a blockbuster successor to Spinraza or an expensive footnote. For the families navigating SMA right now, the early signal is worth paying attention to. For investors, it's worth watching closely, with expectations calibrated accordingly.

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